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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income (loss) available to common stockholders	$ 67,268	$ (4,140)	$ 218,700	$ 119,842
Weighted average shares outstanding-basic (in shares)	206,118,472	170,194,254	205,931,031	163,481,306
Potentially dilutive common shares:
Unvested incentive units (shares)	169,100	0	160,117	150,369
Forward equity offering (shares)	37,884	0	1,847	166,493
Market performance-based awards (shares)	440,800	0	462,632	572,928
Weighted average shares/units outstanding-diluted (shares/units)	206,766,256	170,194,254	206,555,627	164,371,096
Income (loss) per share:
Basic (in dollars per share)	$ 0.33	$ (0.02)	$ 1.06	$ 0.73
Diluted (in dollars per share)	$ 0.33	$ (0.02)	$ 1.06	$ 0.73