National Storage Affiliates Trust Annual report pursuant to Section 13 and 15(d)

Annual report pursuant to Section 13 and 15(d)

DEBT FINANCING - Narrative (Details)

DEBT FINANCING - Narrative (Details)			1 Months Ended	3 Months Ended				12 Months Ended
DEBT FINANCING - Narrative (Details)	Jun. 05, 2018 USD ($)	Jun. 30, 2016 USD ($)	Aug. 31, 2017 USD ($) property	Dec. 31, 2018 USD ($) property agency	Sep. 30, 2018 USD ($) property	Jun. 30, 2018 USD ($) property	Mar. 31, 2018 USD ($) property	Dec. 31, 2018 USD ($) property component agency	Dec. 21, 2018 USD ($)	Jun. 04, 2018 USD ($)
Credit Facility [Member]
Debt Instrument [Line Items]
Covenant compliance, maximum leverage ratio (percent)								60.00%
Covenant compliance, minimum interest coverage ratio								1.5
Covenant compliance, required minimum net worth				$ 682,600,000				$ 682,600,000
Covenant compliance, required minimum net worth, addition to base, percent of equity issuances (percent)				75.00%				75.00%
Covenant compliance, maximum unsecured debt to unencumbered asset ratio (percent)								60.00%
Covenant compliance, unencumbered net operating income to unsecured interest expense ratio								2
Line of Credit Facility, Maximum Borrowing Capacity If Expansion Option Is Exercised				$ 1,300,000,000				$ 1,300,000,000
Line of Credit [Member] \| Credit Facility [Member] \| Revolving line of credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				400,000,000				$ 400,000,000
Extension fee (percent)								0.15%
Remaining borrowing capacity				$ 254,800,000				$ 254,800,000
Effective interest rate (percent)				3.90%				3.90%
Line of Credit [Member] \| Credit Facility [Member] \| Revolving line of credit [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Elective unused borrowing capacity fee (percent)								0.15%
Unused borrowing capacity fee (percent)								0.125%
Line of Credit [Member] \| Credit Facility [Member] \| Revolving line of credit [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Elective unused borrowing capacity fee (percent)								0.25%
Unused borrowing capacity fee (percent)								0.30%
Line of Credit [Member] \| Credit Facility [Member] \| Letter of Credit [Member]
Debt Instrument [Line Items]
Outstanding letters of credit				$ 5,700,000				$ 5,700,000
Unsecured Debt [Member] \| Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 1,000,000,000				$ 1,000,000,000
Number of lender agreement components \| component								5
Unsecured Debt [Member] \| Credit Facility [Member] \| Federal Funds Effective Swap Rate [Member]
Debt Instrument [Line Items]
Borrowing rate spread (percent)								0.50%
Unsecured Debt [Member] \| Credit Facility [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Borrowing rate spread (percent)								1.00%
Unsecured Debt [Member] \| Credit Facility [Member] \| Base Rate [Member]
Debt Instrument [Line Items]
Minimum number of rating agencies required \| agency				2				2
Unsecured Debt [Member] \| Credit Facility [Member] \| Minimum [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Leverage based margin threshold (percent)								1.30%
Elective leverage based margin threshold (percent)								0.85%
Unsecured Debt [Member] \| Credit Facility [Member] \| Minimum [Member] \| Base Rate [Member]
Debt Instrument [Line Items]
Leverage based margin threshold (percent)								0.30%
Elective leverage based margin threshold (percent)								0.00%
Unsecured Debt [Member] \| Credit Facility [Member] \| Maximum [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Leverage based margin threshold (percent)								2.25%
Elective leverage based margin threshold (percent)								2.45%
Unsecured Debt [Member] \| Credit Facility [Member] \| Maximum [Member] \| Base Rate [Member]
Debt Instrument [Line Items]
Leverage based margin threshold (percent)								1.25%
Elective leverage based margin threshold (percent)								1.45%
Unsecured Debt [Member] \| Credit Facility [Member] \| Term Loan A
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 235,000,000				$ 235,000,000
Effective interest rate (percent)				2.91%				2.91%
Unsecured Debt [Member] \| Credit Facility [Member] \| Term Loan B
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 155,000,000				$ 155,000,000
Effective interest rate (percent)				2.94%				2.94%
Unsecured Debt [Member] \| Credit Facility [Member] \| Term Loan C
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 105,000,000				$ 105,000,000
Effective interest rate (percent)				3.71%				3.71%
Unsecured Debt [Member] \| Credit Facility [Member] \| Term Loan D
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 125,000,000				$ 125,000,000
Effective interest rate (percent)				3.79%				3.79%
Unsecured Debt [Member] \| 2023 Term Loan Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 175,000,000									$ 100,000,000
Borrowing capacity increase	200,000,000
Proceeds from lines of credit	75,000,000
Current borrowing capacity	225,000,000
Debt instrument, face amount		$ 100,000,000
Line of Credit Facility, Maximum Borrowing Capacity If Expansion Option Is Exercised	$ 400,000,000
Effective interest rate (percent)				3.13%				3.13%
Unsecured Debt [Member] \| 2023 Term Loan Facility [Member] \| Federal Funds Effective Swap Rate [Member]
Debt Instrument [Line Items]
Borrowing rate spread (percent)								0.50%
Unsecured Debt [Member] \| 2023 Term Loan Facility [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Borrowing rate spread (percent)								1.00%
Unsecured Debt [Member] \| 2023 Term Loan Facility [Member] \| Minimum [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Leverage based margin threshold (percent)								1.30%
Elective leverage based margin threshold (percent)								0.90%
Unsecured Debt [Member] \| 2023 Term Loan Facility [Member] \| Minimum [Member] \| Base Rate [Member]
Debt Instrument [Line Items]
Leverage based margin threshold (percent)		0.30%
Elective leverage based margin threshold (percent)								0.00%
Unsecured Debt [Member] \| 2023 Term Loan Facility [Member] \| Maximum [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Leverage based margin threshold (percent)								1.70%
Elective leverage based margin threshold (percent)								1.75%
Unsecured Debt [Member] \| 2023 Term Loan Facility [Member] \| Maximum [Member] \| Base Rate [Member]
Debt Instrument [Line Items]
Leverage based margin threshold (percent)								0.70%
Elective leverage based margin threshold (percent)								0.75%
Unsecured Debt [Member] \| 2028 Term Loan Facility [Member]
Debt Instrument [Line Items]
Debt instrument, face amount									$ 75,000,000
Line of Credit Facility, Maximum Borrowing Capacity If Expansion Option Is Exercised									$ 125,000,000
Effective interest rate (percent)				4.62%				4.62%
Unsecured Debt [Member] \| 2028 Term Loan Facility [Member] \| Federal Funds Effective Swap Rate [Member]
Debt Instrument [Line Items]
Borrowing rate spread (percent)								0.50%
Unsecured Debt [Member] \| 2028 Term Loan Facility [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Borrowing rate spread (percent)								1.00%
Unsecured Debt [Member] \| 2028 Term Loan Facility [Member] \| Minimum [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Leverage based margin threshold (percent)								1.80%
Elective leverage based margin threshold (percent)								1.40%
Unsecured Debt [Member] \| 2028 Term Loan Facility [Member] \| Minimum [Member] \| Base Rate [Member]
Debt Instrument [Line Items]
Leverage based margin threshold (percent)								0.80%
Elective leverage based margin threshold (percent)								0.40%
Unsecured Debt [Member] \| 2028 Term Loan Facility [Member] \| Maximum [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Leverage based margin threshold (percent)								2.35%
Elective leverage based margin threshold (percent)								2.25%
Unsecured Debt [Member] \| 2028 Term Loan Facility [Member] \| Maximum [Member] \| Base Rate [Member]
Debt Instrument [Line Items]
Leverage based margin threshold (percent)								1.35%
Elective leverage based margin threshold (percent)								1.25%
Mortgages [Member] \| Fixed Rate Mortgages Payable [Member]
Debt Instrument [Line Items]
Effective interest rate (percent)				4.18%				4.18%
Number of self storage properties acquired with assumed mortgages \| property								4
Mortgages [Member] \| Fixed Rate Mortgages Payable [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Effective interest rate (percent)				3.63%				3.63%
Mortgages [Member] \| Fixed Rate Mortgages Payable [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Effective interest rate (percent)				5.00%				5.00%
Secured Debt [Member] \| Fixed Rate Mortgages Payable [Member]
Debt Instrument [Line Items]
Debt instrument, face amount			$ 84,900,000
Number of properties used to secure debt \| property			22
Debt instrument, fixed interest rate (percent)			4.14%
2018 Acquisitions [Member]
Debt Instrument [Line Items]
Liabilities assumed, mortgages				$ 0	$ 0	$ 0	$ 7,581,000	$ 7,581,000
Number of self storage properties acquired with assumed mortgages \| property				7	13	12	25	57