Identified Intangible Liabilities, Net - Summary of Amortization Expense on Below Market Leases (Detail) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Intangible Liabilities [Abstract]
2020	$ 207,000
2021	243,000
2022	217,000
2023	207,000
2024	161,000
Thereafter	474,000
Total	$ 1,509,000	$ 1,601,000

Finite Lived Intangible Liabilities Amortization Expenses After Year Five

No definition available.

Name:	gahr_FiniteLivedIntangibleLiabilitiesAmortizationExpensesAfterYearFive
Namespace Prefix:	gahr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Finite Lived Intangible Liabilities Amortization Expenses Remainder Of Fiscal Year

+ References

No definition available.

+ Details

Name:	gahr_FiniteLivedIntangibleLiabilitiesAmortizationExpensesRemainderOfFiscalYear
Namespace Prefix:	gahr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Finite Lived Intangible Liabilities Amortization Expenses Year Five

+ References

No definition available.

+ Details

Name:	gahr_FiniteLivedIntangibleLiabilitiesAmortizationExpensesYearFive
Namespace Prefix:	gahr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Finite Lived Intangible Liabilities Amortization Expenses Year Four

+ References

No definition available.

+ Details

Name:	gahr_FiniteLivedIntangibleLiabilitiesAmortizationExpensesYearFour
Namespace Prefix:	gahr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Finite Lived Intangible Liabilities Amortization Expenses Year Three

+ References

No definition available.

+ Details

Name:	gahr_FiniteLivedIntangibleLiabilitiesAmortizationExpensesYearThree
Namespace Prefix:	gahr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Finite Lived Intangible Liabilities Amortization Expenses Year Two

+ References

No definition available.

+ Details

Name:	gahr_FiniteLivedIntangibleLiabilitiesAmortizationExpensesYearTwo
Namespace Prefix:	gahr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Intangible Liabilities [Abstract]

+ References

No definition available.

+ Details

Name:	gahr_IntangibleLiabilitiesAbstract
Namespace Prefix:	gahr_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents a liability associated with the acquisition of an off-market lease when the terms of the lease are unfavorable to the market terms for the lease at the date of acquisition.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.24)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_OffMarketLeaseUnfavorable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant