Other Data (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Net income	$ 23,092	$ 85,571	$ 69,436
Reconciling items to taxable income:
Depreciation and amortization	46,426	38,260	30,457
Gain or loss on disposition of depreciable assets	1,570	(32,103)	1,659
Impairments	0	121	687
Straight-line rent	(4,551)	(7,101)	(8,833)
Receivable allowances	1,680	2,067	571
Stock-based compensation	1,855	1,301	7,518
Other	6,552	2,236	4,304
Reconciling items to taxable income, total	53,532	4,781	36,363
Taxable income	76,624	90,352	105,799
Dividends paid	$ 142,327	$ 131,759	$ 120,266