Income per Share (Summary of Basic and Diluted Earnings per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income available to common stockholders	$ 187,330	$ 38,522	$ 254,406	$ 257,305
Weighted average shares/units outstanding-basic (shares/units)	147,397,853	135,832,503	146,930,939	135,782,831
Potentially dilutive common shares:
Stock options (shares)	10,424	19,983	9,721	20,629
Unvested incentive units (shares)	82,184	86,190	75,049	65,752
Forward equity offering (shares)	1,264,749	0	2,611	0
Series I Cumulative Redeemable Preferred Stock (shares)	0	1,703,182	0	567,727
Market performance-based awards (shares)	629,661	618,078	636,864	483,538
Weighted average shares/units outstanding-diluted (shares/units)	149,384,871	138,259,936	147,655,184	136,920,477
Income per share:
Basic ($ per share/unit)	$ 1.27	$ 0.28	$ 1.73	$ 1.89
Diluted ($ per share/unit)	$ 1.25	$ 0.28	$ 1.72	$ 1.88