The amount of cash dividends paid per share to common shareholders.

No definition available.

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Represents the impaired real estate assets as of the end of the reporting period that are valued by the entity at fair value as of the balance sheet date.

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The maximum original maturity period for which highly liquid investments will be considered cash and cash equivalents.

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The number of properties classified as held for sale and reported as discontinued operations.

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The number of properties that were reclassified from held for sale to held and used because they no longer met the criteria to be held for sale.

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The number of properties that were sold during the year that previously did not meet the criteria to be classified as held for sale whose gain was reported in continuing operations.

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Amount of ordinary cash dividend paid during the period for each share of common stock outstanding.

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Amount of decrease to current year's net earnings resulting from the correction in the current year of a misstatement made in the prior year's financial statements.

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Cash outflow in the form of a special dividend to common shareholders, preferred shareholders and noncontrolling interests, generally out of earnings.

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No definition available.

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Represents the percentage of annual assumed average rent increases used as an unobservable input to measure the fair value.

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Amount of special cash dividend paid during the period for each share of common stock outstanding.

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The amount of taxes withheld related to a property acquisition.

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Fair value portion of amount due from customers or clients for goods or services, including trade receivables, that have been delivered or sold in the normal course of business, and amounts due from others, including related parties.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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-Topic 360

-SubTopic 10

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-Paragraph 4

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The designation of funds furnished by a borrower to a lender to assure future payments of the borrower's real estate taxes and insurance obligations with respect to a mortgaged property. Escrow deposits may be made for a variety of other purposes such as earnest money and contingent payments. This element excludes replacement reserves which are an escrow separately provided for within the US GAAP taxonomy.

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-Name Accounting Standards Codification

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-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.10)

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Period the instrument, asset or liability is expected to be outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (e)

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Ratio of the net operating income produced by an asset and its capital cost (original prices paid to buy the asset), used as an input to measure fair value.

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-SubTopic 10

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-Paragraph 2

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Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

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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.

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-Section 45

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- Definition

Amount of judgment or settlement awarded to (against) the entity in respect of litigation.

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No definition available.

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Cash outflow in the form of capital distributions and dividends to common shareholders, preferred shareholders and noncontrolling interests.

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

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-Paragraph 15

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-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585

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Cash outflow in the form of ordinary dividends to common shareholders, preferred shareholders and noncontrolling interests, generally out of earnings.

+ References

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Fair value portion of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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-Paragraph 1

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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No definition available.

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The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. This element is for unclassified presentations; for classified presentations there is a separate and distinct element.

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-Name Regulation S-X (SX)

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-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.1)

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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended			3 Months Ended
	Mar. 31, 2014	Dec. 31, 2014 Property	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2013
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Legal settlements received			$ 3,126,000us-gaap_LitigationSettlementAmount
Number of real estate properties held for sale		20
Number of properties sold		4
Gain from sale of properties		1,223,000us-gaap_GainLossOnSaleOfProperties
Number of properties reclassified		8
Impairment charges		21,534,000us-gaap_AssetImpairmentCharges	13,425,000us-gaap_AssetImpairmentCharges	13,942,000us-gaap_AssetImpairmentCharges
Maturity period of liquid investments		3 months
Restricted cash		713,000	1,000,000
Escrow account		463,000us-gaap_EscrowDeposit
Tax with holdings related to a property acquisition		250,000,000
Stock based compensation expenses		917,000	971,000	757,000
Cash dividends		28,675,000us-gaap_PaymentsOfDividends	24,419,000us-gaap_PaymentsOfDividends	8,404,000us-gaap_PaymentsOfDividends
Cash dividends per share		$ 0.850gty_CashDividendsPaidPerShare	$ 0.725gty_CashDividendsPaidPerShare
Payment of regular quarterly cash dividend		26,990,000us-gaap_PaymentsOfOrdinaryDividends
Payment of special cash dividend		1,685,000gty_PaymentOfSpecialDividend
Regular quarterly cash dividends paid per share		$ 0.80
Special cash dividends paid per share		$ 0.05gty_SpecialCashDividendPerShareCashPaid
Adjustment which decreased net earnings	420,000gty_OutOfPeriodAdjustments
Buildings and Improvements [Member] \| Minimum [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Property plant and equipment useful life		16 years
Buildings and Improvements [Member] \| Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Property plant and equipment useful life		25 years
USTs [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Property plant and equipment useful life		10 years
Estimated Sale Price Method [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impairment charges		4,916,000
Estimated fair value		21,534,000
Discounted Cash Flow Method [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impairment charges		8,117,000
Estimated fair value		21,534,000
Accumulation of Asset Retirement Cost Method [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impairment charges		8,501,000
Estimated fair value		21,534,000
Litigation Funding Agreement [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Legal settlements received					25,096,000
Stock Options [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Anti-dilutive securities Excluded from calculation of EPS		5,000	5,000	5,000
Finance Leases Financing Receivable [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impairment charges		0	0	0
Level 3 [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Assumed holding periods for unobservable inputs		15 years
Assumed annual average rent increases for unobservable inputs		2.00%
Rate of income capitalization for unobservable inputs		8.00%
Cash flows discounted rate for unobservable inputs		7.00%
Level 3 [Member] \| Fair Value, Measurements, Recurring [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Accounts receivable measured at fair value				2,972,000
Level 3 [Member] \| Fair Value, Measurements, Nonrecurring [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impaired real estate assets measured at fair value		$ 9,266,000	$ 9,590,000