Schedule III - Real Estate and Accumulated Depreciation - Reconciliation of Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
SEC Schedule III, Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance, beginning of year	$ 556,546	$ 465,584	$ 377,552
Depreciation expense	119,490	106,343	108,319
Disposals	(19,136)	(15,381)	(20,287)
Balance, end of year	$ 656,900	$ 556,546	$ 465,584