Discontinued Operations and Assets Held For Sale - Additional Information (Detail)	12 Months Ended
Dec. 31, 2018 USD ($) Portfolio	Dec. 31, 2017 USD ($) Portfolio
Discontinued Operations And Disposal Groups [Abstract]
Gain from sale of properties \| $	$ 3,888,000	$ 1,025,000
Number of whole properties sold not meeting criteria of discontinued operations recognized gain included in continuing operations \| Portfolio	9	12
Number of partial properties sold not meeting criteria of discontinued operations recognized gain included in continuing operations \| Portfolio		1
Gain on property condemnations \| $	$ 60,000	$ 16,000

Number of partial properties sold not meeting criteria of discontinued operations recognized gain included in continuing operations.

No definition available.

+ Details

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- Definition

Number of whole properties sold not meeting criteria of discontinued operations recognized gain included in continuing operations.

+ References

No definition available.

+ Details

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Namespace Prefix:	gty_
Data Type:	xbrli:integerItemType
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- References

No definition available.

+ Details

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- Definition

The gain (loss) is the pre-tax difference between the net condemnation award and the entity's adjusted basis of the condemned property.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

+ Details

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- Definition

The difference between the carrying value and the sale price of real estate or properties that were intended to be sold or held for capital appreciation or rental income. This element refers to the gain (loss) included in earnings and not to the cash proceeds of the sale. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2941-110230

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2443-110228

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