General - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended			9 Months Ended					3 Months Ended	9 Months Ended		3 Months Ended	9 Months Ended	0 Months Ended	3 Months Ended		3 Months Ended	9 Months Ended
	Jun. 30, 2014 Property	Sep. 30, 2014 Property	Mar. 31, 2014	Sep. 30, 2013	Sep. 30, 2014 Property	Sep. 30, 2013	Sep. 30, 2014 Estimated Sale Price Method [Member]	Sep. 30, 2014 Discounted Cash Flow Method [Member]	Sep. 30, 2014 Accumulation of Asset Retirement Cost Method [Member]	Sep. 30, 2013 Litigation Funding Agreement [Member]	Sep. 30, 2014 Stock Options [Member]	Sep. 30, 2013 Stock Options [Member]	Sep. 30, 2013 Reclassifications [Member]	Sep. 30, 2013 Reclassifications [Member]	Jun. 30, 2014 Loan in Default for Nonpayment [Member] MortgageLoan	Sep. 30, 2014 Loan in Default for Nonpayment [Member]	Jun. 30, 2014 Loan in Default for Nonpayment [Member]	Sep. 30, 2014 Finance Leases Financing Receivable [Member]	Sep. 30, 2013 Finance Leases Financing Receivable [Member]	Sep. 30, 2014 Level 3 [Member]	Dec. 31, 2012 Level 3 [Member] Fair Value, Measurements, Recurring [Member]	Sep. 30, 2014 Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member]	Dec. 31, 2013 Level 3 [Member] Fair Value, Measurements, Nonrecurring [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Legal settlements received				$ 3,126,000		$ 3,126,000				$ 25,096,000
Accounts receivable measured at fair value																					2,972,000
Impaired real estate assets measured at fair value																						1,758,000	9,590,000
Number of real estate properties held for sale	46
Number of properties reclassified		2			2
Number of properties sold		2
Gain from sale of properties		1,389,000
Impairment charges		2,906,000		3,265,000	6,583,000	7,717,000	3,103,000	518,000	2,962,000									0	0
Estimated fair value							6,583,000	6,583,000	6,583,000
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%
Outstanding loan amount																	475,000
Number of mortgage loans															1
Allowance for mortgages receivable																	133,000
Partial amount received on mortgage loan																75,000
Issuance of new mortgage loan					400,000
Allowance for loan losses written off					35,000
Anti-dilutive securities Excluded from calculation of EPS											5,000	5,000
Cash dividends					21,925,000	17,680,000
Cash dividends per share					$ 0.650	$ 0.525
Payment of regular quarterly cash dividend					20,240,000	20,240,000
Payment of special cash dividend					1,685,000	1,685,000
Regular quarterly cash dividends paid per share					$ 0.60	$ 0.60
Special cash dividends paid per share					$ 0.05	$ 0.05
Rental property expenses		5,538,000		7,085,000	17,420,000	21,525,000							933,000	1,726,000
Adjustment which decreased net earnings			$ 420,000