Schedule III - Real Estate Investments (Summary of Historical Cost and Accumulated Depreciation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property
Balance, beginning of period	$ 2,357,322	$ 1,964,857	$ 1,583,153
Disposals	(43,616)	(18,198)	(8,946)
Additions (acquisitions and improvements)	499,150	410,663	390,650
Balance, end of period	2,812,856	2,357,322	1,964,857
Accumulated depreciation
Balance, beginning of period	(394,823)	(317,834)	(239,936)
Disposals	30,139	13,970	6,761
Additions (depreciation and amortization expense)	(102,960)	(90,959)	(84,659)
Balance, end of period	$ (467,644)	$ (394,823)	$ (317,834)