Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net earnings	$ 47,706	$ 47,186	$ 38,411
Adjustments to reconcile net earnings to net cash flow provided by operating activities:
Depreciation and amortization expense	23,636	19,089	19,170
Impairment charges	6,170	9,321	12,814
(Gains) loss on dispositions of real estate
Continuing operations	(3,948)	(1,041)	(6,390)
Discontinued operations			178
Deferred rent receivable	(4,112)	(3,644)	(4,516)
Allowance (recoveries) for uncollectible accounts	470	205	(448)
Amortization of above-market and below-market leases	(808)	(522)	(569)
Amortization of debt issuance costs	871	771	851
Accretion expense	2,409	3,448	4,107
Stock-based compensation expense	1,777	1,350	1,426
Changes in assets and liabilities:
Accounts receivable	(814)	(1,295)	(2,383)
Prepaid expenses and other assets	(708)	489	445
Environmental remediation obligations	(11,210)	(19,798)	(24,640)
Accounts payable and accrued liabilities	1,907	1,183	(1,582)
Net cash flow provided by operating activities	63,346	56,742	36,874
CASH FLOWS FROM INVESTING ACTIVITIES:
Property acquisitions	(77,972)	(214,000)	(7,688)
Capital expenditures	(3,794)	(434)	(298)
Addition to construction in progress	(2,657)	(1,255)	(406)
Proceeds from dispositions of real estate
Continuing operations	3,303	2,739	3,957
Discontinued operations			88
Deposits for property acquisitions	(430)	2,346	(2,206)
Amortization of investment in direct financing leases	3,015	2,511	2,001
(Issuance) of notes and mortgages receivable	(530)
Collection of notes and mortgages receivable	3,134	1,876	17,532
Net cash flow (used in) provided by investing activities	(75,931)	(206,217)	12,980
CASH FLOWS FROM FINANCING ACTIVITIES:
Borrowings under credit agreements	95,000	135,000	8,000
Repayments under credit agreements	(130,000)	(105,000)	(27,000)
Proceeds from senior unsecured notes	100,000	50,000
Payments of capital lease obligations	(468)	(342)	(236)
Repayment of mortgage payable			(400)
Payments of cash dividends	(50,503)	(39,299)	(36,231)
Payments of debt issuance costs	(3,393)	(157)
Security deposits received (refunded)	(260)	247	260
Payments in settlement of restricted stock units		(1,195)	(290)
Net cash flow provided by (used in) financing activities	40,514	157,094	(41,011)
Change in cash, cash equivalents and restricted cash	27,929	7,619	8,843
Cash, cash equivalents and restricted cash at beginning of year	20,813	13,194	4,351
Cash, cash equivalents and restricted cash at end of year	48,742	20,813	13,194
Supplemental disclosures of cash flow information Cash paid during the period for:
Interest	20,790	16,435	15,707
Income taxes	244	(195)	368
Environmental remediation obligations	9,891	12,944	17,633
Non-cash transactions
Dividends declared but not yet paid	14,495	12,846	9,742
Issuance of notes and mortgages receivable related to property dispositions	3,743	1,505	1,814
Equity Offering [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net		104,312
ATM Program [Member]
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net	$ 30,138	$ 13,528	$ 14,886