CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Income	$ 82,929,000	$ 71,892,000	$ 156,850,000
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	22,354,000	21,547,000	20,577,000
Impairment expense	1,530,000	228,000	0
Gain on disposal of land, building, and equipment	(15,271,000)	(10,532,000)	(16,623,000)
Gain on exchange of non-financial assets	(228,000)	0	0
Amortization of financing costs	1,834,000	2,144,000	1,592,000
Stock-based compensation expense	3,967,000	2,676,000	1,550,000
Deferred income taxes	0	(196,000)	(80,685,000)
Changes in assets and liabilities:
Derivative assets and liabilities	29,000	145,000	(609,000)
Straight-line rent adjustment	(9,288,000)	(9,536,000)	(10,095,000)
Rent received in advance	(6,686,000)	321,000	34,000
Other assets and liabilities	(288,000)	220,000	(1,652,000)
Net cash provided by operating activities	80,882,000	78,909,000	70,939,000
Cash flows - investing activities
Purchases of operating real estate	(268,266,000)	(95,112,000)	(83,263,000)
Net proceeds from sale of operating real estate	21,139,000	15,645,000	24,091,000
Advance deposits on acquisition of operating real estate	81,000	(947,000)	(150,000)
Net cash used in investing activities	(247,046,000)	(80,414,000)	(59,322,000)
Cash flows - financing activities
Proceeds from issuance of senior notes	100,000,000	125,000,000	0
Payment of deferred financing costs	(1,481,000)	(5,500,000)	0
Proceeds from revolving credit facility	25,000,000	36,000,000	45,000,000
Repayment of revolving credit facility	(25,000,000)	(81,000,000)	0
Payment of dividend to shareholders	(69,494,000)	(58,695,000)	(121,604,000)
Distribution to non-controlling interests	(456,000)	(460,000)	0
Redemption of non-controlling interests	0	(988,000)	0
Repayment of debt assumed in purchase of real estate investments	0	(2,305,000)	(7,083,000)
Shares withheld for taxes upon vesting	393,000	0	0
Net cash provided by (used in) financing activities	190,034,000	44,197,000	(83,047,000)
Net increase (decrease) in cash and cash equivalents, including restricted cash	23,871,000	42,692,000	(71,430,000)
Cash and cash equivalents, including restricted cash, beginning of year	69,371,000	26,643,000	98,073,000
Cash and cash equivalents, including restricted cash, ending of year	93,242,000	69,371,000	26,643,000
Supplemental disclosures:
Interest paid	14,180,000	14,102,000	13,493,000
Taxes paid	470,000	561,000	2,168,000
Non - cash investing and financing activities:
Dividends payable	19,580,000	16,843,000	14,519,000
Debt assumed in acquisition of real estate investments	0	2,305,000	7,083,000
Change in fair value of derivative instruments	993,000	4,152,000	1,149,000
Operating partner units issued in exchange for real estate investments	0	3,609,000	5,039,000
At-The-Market Offering
Cash flows - financing activities
Net proceeds form issuance of stock	65,533,000	32,145,000	640,000
Equity Offering
Cash flows - financing activities
Net proceeds form issuance of stock	$ 96,325,000	$ 0	$ 0