Consolidated Statements of Cash Flows (Unaudited) - USD ($)	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net earnings	$ 34,516,000	$ 34,150,000
Adjustments to reconcile net earnings to net cash flow provided by operating activities:
Depreciation and amortization expense	17,569,000	13,465,000
Impairment charges	4,808,000	7,044,000
(Gain) loss on dispositions of real estate	(3,636,000)	(339,000)
Deferred rent receivable	(3,214,000)	(2,540,000)
Allowance for uncollectible accounts	364,000	200,000
Accretion expense	1,837,000	2,621,000
Amortization of above-market and below-market leases	(624,000)	(345,000)
Amortization of loan origination costs	636,000	578,000
Stock-based compensation	1,309,000	996,000
Changes in assets and liabilities:
Accounts receivable	(392,000)	(67,000)
Prepaid expenses and other assets	(383,000)	(77,000)
Environmental remediation obligations	(7,516,000)	(15,752,000)
Accounts payable and accrued liabilities	1,213,000	265,000
Net cash flow provided by operating activities	46,487,000	40,199,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Property acquisitions	(74,714,000)	(143,885,000)
Capital expenditures	(878,000)	(307,000)
Addition to construction in progress	(2,050,000)	(839,000)
Proceeds from dispositions of real estate	1,641,000	2,410,000
Deposits for property acquisitions	(300,000)	1,711,000
Amortization of investment in direct financing leases	2,210,000	1,836,000
(Issuance) of notes and mortgages receivable	(242,000)
Collection of notes and mortgages receivable	2,855,000	1,498,000
Net cash flow (used in) investing activities	(71,478,000)	(137,576,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Borrowings under credit agreement	70,000,000	65,000,000
Repayments under credit agreement	(125,000,000)	(95,000,000)
Proceeds from senior unsecured notes	100,000,000	50,000,000
Payment of loan origination costs	(3,393,000)	(157,000)
Payments of cash dividends	(37,681,000)	(28,457,000)
Payments in settlement of restricted stock units		(1,195,000)
Other	(395,000)	(5,000)
Net cash flow provided by financing activities	24,183,000	103,043,000
Change in cash, cash equivalents and restricted cash	(808,000)	5,666,000
Cash, cash equivalents and restricted cash at beginning of period	20,813,000	13,194,000
Cash, cash equivalents and restricted cash at end of period	20,005,000	18,860,000
Supplemental disclosures of cash flow information Cash paid during the period for:
Interest	15,360,000	11,834,000
Income taxes	224,000	36,000
Environmental remediation obligations	6,836,000	9,636,000
Non-cash transactions:
Dividends declared but not yet paid	13,145,000	11,165,000
Issuance of notes and mortgages receivable related to property dispositions	3,313,000	432,000
Equity Offering [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net		104,312,000
ATM Program [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net	$ 20,652,000	$ 8,545,000