Leases - Future Contractual Minimum Annual Rentals Receivable (Parenthetical) (Detail) (USD $)	Dec. 31, 2014
Future Minimum Lease Payments For Capital Leases And Operating Leases [Abstract]
Amount of future minimum annual rental payments receivable under subleases	$ 74,559,000

Amount of future minimum annual rental payments receivable under subleases.

No definition available.

Name:	gty_FutureMinimumLeasePaymentsReceivableUnderSubleases
Namespace Prefix:	gty_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant