Summary of Significant Accounting Policies - Earnings Per Common Share, Computation of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Net income attributable to common stockholders	$ 82,403	$ 118,088	$ 83,044	$ 82,592	$ 8,675	$ 71,718	$ 55,339	$ 53,742	$ 366,127	$ 189,474	$ 178,355
Earnings and dividends allocated to participating securities									(792)	(601)	(490)
Earnings for basic computations									365,335	188,873	177,865
Earnings and dividends allocated to participating securities									792	0	0
Income allocated to noncontrolling interest - Preferred Operating Partnership (Series A Units) and Operating Partnership									0	14,790	13,575
Fixed component of income allocated to noncontrolling interest - Preferred Operating Partnership (Series A Units)									0	(5,088)	(5,586)
Net income for diluted computations									$ 366,127	$ 198,575	$ 185,854
Weighted average common shares outstanding:
Average number of common shares outstanding - basic (in shares)									125,087,554	119,816,743	115,713,807
OP Units									0	5,451,357	4,335,837
Series A Units									0	875,480	961,747
Unvested restricted stock awards included for treasury stock method									299,585	0	0
Shares related to exchangeable senior notes and dilutive stock options									560,937	775,289	423,876
Average number of common shares outstanding - diluted (in shares)									125,948,076	126,918,869	121,435,267
Earnings per common share
Basic (in dollars per share)	$ 0.65	$ 0.94	$ 0.66	$ 0.66	$ 0.07	$ 0.58	$ 0.47	$ 0.46	$ 2.92	$ 1.58	$ 1.54
Diluted (in dollars per share)	$ 0.65	$ 0.93	$ 0.66	$ 0.66	$ 0.07	$ 0.58	$ 0.47	$ 0.46	$ 2.91	$ 1.56	$ 1.53