Schedule III - Real Estate and Accumulated Depreciation (Details) - Reconciliation of Real Estate - Owned Subject to Operating Leases - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
SEC Schedule III, Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance	$ 2,296,617	$ 1,785,898	$ 1,372,434
Property improvements during the year	41,359	28,104	27,515
Properties acquired during the year	354,035	485,853	416,298
Properties sold during the year	0	0	(23,676)
Assets written off during the year	(4,993)	(3,238)	(6,673)
Balance	$ 2,687,018	$ 2,296,617	$ 1,785,898