Summary of Significant Accounting Policies - Additional Information (Detail)			3 Months Ended		12 Months Ended
	Nov. 25, 2015 USD ($)	Aug. 03, 2015 USD ($) Tenants	Dec. 31, 2015 USD ($) Property $ / shares	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) Property $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) shares
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of real estate properties held for sale | Property			5		5
Number of properties sold previously held for sale | Property					14
Gain from sale of properties					$ 1,333,000
Loss on partial condemnation					51,000
Loss on capital lease termination					$ 8,000
Number of properties sold | Property					70
Number of properties reclassified | Property			1		1
Impairment charges					$ 17,361,000	$ 21,534,000	$ 13,425,000
Total consideration for properties sold including seller financing		$ 15,000,000
Maturity period of liquid investments					3 months
Restricted cash			$ 409,000		$ 409,000	713,000
Escrow account						463,000
Tax with holdings related to a property acquisition						250,000,000
Stock based compensation expenses					1,090,000	917,000	971,000
Cash dividends	$ 2,941,000				$ 35,150,000	$ 28,675,000	$ 24,419,000
Cash dividends per share | $ / shares					$ 1.04	$ 0.85
Payment of regular quarterly cash dividend					$ 30,425,000	$ 26,990,000
Payment of special cash dividend					$ 4,725,000	$ 1,685,000
Regular quarterly cash dividends paid per share | $ / shares					$ 0.90	$ 0.80
Special cash dividends paid per share | $ / shares					$ 0.14	$ 0.05
Adjustment which decreased net earnings				$ 420,000
Overstatement [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Overstated non-cash impairment charges from continuing operations			613,000
Overstated non-cash impairment charges from discontinued operations			$ 401,000
Understatement [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impact of overstatement on earnings per share | $ / shares			$ 0.03
Understatement of net earnings			$ 1,014,000
Properties Previously Classified Held for Sale [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Gain from sale of properties					$ 339,000
Stock Options [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Anti-dilutive securities Excluded from calculation of EPS | shares					5,000	5,000	5,000
Direct Financing Leases Financing Receivable [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impairment charges					$ 0	$ 0	$ 0
Leaseholds and Leasehold Improvements [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Sale of leasehold improvement and recognized a gain					$ 998,000
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					$ 17,361,000
Estimated fair value			8,776,000		8,776,000
Discounted Cash Flow Method [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impairment charges					17,361,000
Estimated fair value			842,000		842,000
Accumulation of Asset Retirement Cost Method [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impairment charges					17,361,000
Estimated fair value			7,743,000		$ 7,743,000
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, Nonrecurring [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Impaired real estate assets measured at fair value			1,264,000		$ 1,264,000	$ 9,266,000
Ramoco Affiliates [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of properties sold to Ramoco affiliates that were previously included in the Ramoco lease | Tenants		48
Accounts Payable and Accrued Liabilities [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Deferred gain on sale of property			$ 3,900,000		$ 3,900,000