Description of Business - Additional Information (Detail)	Mar. 31, 2021 Property State
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of properties in portfolio \| Property	960
Number of states in which our properties are located \| State	35

The number of states in which the company's properties, comprised of those that are owned and those that are leased from third party landlords, are located.

No definition available.

Name:	gty_NumberOfStatesInWhichPropertiesAreLocated
Namespace Prefix:	gty_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant