Income per Share (Summary of Basic and Diluted Earnings per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income available to common stockholders	$ 65,134	$ 57,837	$ 151,432	$ 123,982
Weighted average shares outstanding-basic (in shares)	205,956,005	160,832,889	205,835,757	160,069,201
Potentially dilutive common shares:
Unvested incentive units (shares)	151,265	161,553	150,864	151,807
Forward equity offering (shares)	0	216,526	0	251,119
Market performance-based awards (shares)	455,809	570,899	473,549	587,400
Weighted average shares/units outstanding-diluted (shares/units)	206,563,079	161,781,867	206,460,170	161,059,527
Income per share:
Basic (in dollars per share)	$ 0.32	$ 0.36	$ 0.74	$ 0.77
Diluted (in dollars per share)	$ 0.32	$ 0.36	$ 0.73	$ 0.77