Gladstone Commercial Corporation Quarterly report pursuant to Section 13 or 15(d)

Real Estate and Intangible Assets - Carrying Value of Intangible Assets and Accumulated Amortization (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Below market leases and deferred revenue, gross	$ (43,152)	$ (38,319)
Below market leases and deferred revenue, accumulated amortization	20,693	17,686
Lease Intangibles
Finite-Lived Intangible Assets [Line Items]
Lease Intangibles	251,567	241,229
Accumulated Amortization	(139,785)	(123,850)
In-place leases
Finite-Lived Intangible Assets [Line Items]
Lease Intangibles	102,796	99,254
Accumulated Amortization	(60,713)	(54,168)
Leasing costs
Finite-Lived Intangible Assets [Line Items]
Lease Intangibles	78,755	73,707
Accumulated Amortization	(42,536)	(37,801)
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Lease Intangibles	70,016	68,268
Accumulated Amortization	(36,536)	(31,881)
Above market leases
Finite-Lived Intangible Assets [Line Items]
Lease Intangibles	15,460	15,076
Accumulated Amortization	$ (11,312)	$ (10,670)