Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
CASH FLOWS FROM OPERATING ACTIVITIES:
Net earnings	$ 37,410,000	$ 23,418,000	$ 70,011,000
Depreciation and amortization expense
Continuing operations	16,974,000	10,549,000	9,346,000
Discontinued operations			581,000
Impairments	17,361,000	21,534,000	13,425,000
Gains on dispositions of real estate
Continuing operations	(2,272,000)	(1,223,000)
Discontinued operations	(339,000)	(8,995,000)	(45,505,000)
Deferred rent receivable, net of allowance	(4,401,000)	(4,156,000)	(4,445,000)
Bad debt expense (recoveries)	1,089,000	1,278,000	(20,854,000)
Amortization of above-market and below-market leases	(1,496,000)	(28,000)	160,000
Amortization of credit agreement and senior unsecured notes origination costs	1,150,000	1,068,000	1,650,000
Accretion expense	4,829,000	3,046,000	3,214,000
Stock-based employee compensation expense	1,090,000	917,000	971,000
Changes in assets and liabilities:
Accounts receivable	(1,546,000)	(730,000)	20,847,000
Prepaid expenses and other assets	(189,000)	3,934,000	(201,000)
Environmental remediation obligations	(23,485,000)	(16,368,000)	(15,611,000)
Accounts payable and accrued liabilities	3,513,000	(5,007,000)	10,089,000
Net cash flow provided by operating activities	49,688,000	29,237,000	43,678,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Property acquisitions and capital expenditures	(219,526,000)	(17,238,000)	(67,174,000)
Investment in direct financing leases			(6,267,000)
Proceeds from dispositions of real estate
Continuing operations	5,604,000	4,776,000
Discontinued operations	1,424,000	15,289,000	66,349,000
Change in cash held for property acquisitions	2,844,000	16,226,000	(16,467,000)
Change in restricted cash	304,000	287,000	(1,000,000)
Addition to construction in progress	(687,000)
Amortization of investment in direct financing leases	1,666,000	1,382,000	1,025,000
Issuance of notes, mortgages and other receivables			(4,138,000)
Collection of notes and mortgages receivable	3,647,000	2,783,000	20,825,000
Net cash flow (used in) / provided by investing activities	(204,724,000)	23,505,000	(6,847,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Borrowings under prior credit agreement	14,000,000	3,000,000	130,400,000
Repayments under prior credit agreement	(39,000,000)	(36,000,000)	(222,690,000)
Borrowings under new credit agreement	172,000,000
Repayments under new credit agreement	(28,000,000)
Borrowings under senior unsecured notes	75,000,000		100,000,000
Repayments under term loan			(22,030,000)
Payments of capital lease obligations	(249,000)	(255,000)	(220,000)
Principal payments of mortgage notes	(50,000)	(50,000)
Payments of cash dividends	(35,150,000)	(28,675,000)	(24,419,000)
Payments of loan origination costs	(2,432,000)		(2,842,000)
Cash paid in settlement of restricted stock units	(65,000)
Security deposits (refunded) received	(187,000)	314,000	129,000
Net cash flow provided by / (used in) financing activities	155,867,000	(61,666,000)	(41,672,000)
Change in cash and cash equivalents	831,000	(8,924,000)	(4,841,000)
Cash and cash equivalents at beginning of year	3,111,000	12,035,000	16,876,000
Cash and cash equivalents at end of year	3,942,000	3,111,000	12,035,000
Supplemental disclosures of cash flow information Cash paid during the period for:
Interest paid	12,643,000	8,735,000	9,563,000
Income taxes	341,000	316,000	173,000
Environmental remediation obligations	19,123,000	13,448,000	12,396,000
Non-cash transactions
Issuance of notes and mortgages receivable related to property dispositions	17,876,000	8,278,000	$ 8,714,000
Mortgage payable, net related to property acquisition		$ 390,000
Accrued construction in progress	$ 268,000