Schedule III - Real Estate Investments (Summary of Historical Cost and Accumulated Depreciation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property
Balance, beginning of period	$ 1,583,153	$ 1,177,582	$ 905,735
Disposals	(8,946)	(5,617)	(54)
Additions (acquisitions and improvements)	390,650	411,188	271,901
Balance, end of period	1,964,857	1,583,153	1,177,582
Accumulated depreciation
Balance, beginning of period	(239,936)	(180,167)	(137,725)
Disposals	6,761	1,377	39
Additions (depreciation and amortization expense)	(84,659)	(61,146)	(42,481)
Balance, end of period	$ (317,834)	$ (239,936)	$ (180,167)