Identified Intangible Assets, Net - Summary of Identified Intangibles, Net (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Identified intangible assets, net	$ 153,523	$ 154,687
Weighted average remaining life	9 years 8 months 12 days	9 years 8 months 12 days
Certificates Of Need [Member]
Finite-Lived Intangible Assets [Line Items]
Unamortized intangible assets	$ 96,595	$ 96,589
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Unamortized intangible assets	30,787	30,787
In-Place Leases [Member]
Finite-Lived Intangible Assets [Line Items]
Amortized intangible assets	22,735	23,760
Finite-Lived Intangible Assets, Accumulated Amortization	$ 22,504	$ 22,019
Weighted average remaining life	9 years 3 months 18 days	9 years 4 months 24 days
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Amortized intangible assets	$ 2,317	$ 2,354
Finite-Lived Intangible Assets, Accumulated Amortization	$ 523	$ 486
Weighted average remaining life	15 years 4 months 24 days	15 years 8 months 12 days
Above-Market Leases [Member]
Finite-Lived Intangible Assets [Line Items]
Amortized intangible assets	$ 948	$ 1,032
Finite-Lived Intangible Assets, Accumulated Amortization	$ 1,740	$ 1,975
Weighted average remaining life	4 years 6 months	4 years 7 months 6 days
Internally Developed Technology and Software [Member]
Finite-Lived Intangible Assets [Line Items]
Amortized intangible assets	$ 141	$ 165
Finite-Lived Intangible Assets, Accumulated Amortization	$ 329	$ 305
Weighted average remaining life	1 year 4 months 24 days	1 year 8 months 12 days

Griffin-American Healthcare REIT III, Inc. 10-Q