Income per Share (Summary of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income available to common stockholders	$ 31,230	$ 67,268	$ 65,134	$ 86,298	$ 53,306	$ (4,140)	$ 57,837	$ 66,145	$ 249,930	$ 173,148	$ 332,088
Weighted average units outstanding—basic (in shares)									206,035,408	174,059,386	149,953,662
Potentially dilutive common shares:
Stock options (in shares)									0	0	9,726
Unvested incentive units (in shares)									141,260	141,136	71,031
Forward equity offering (in shares)									33,315	124,527	3,990
Market performance-based awards (in shares)									463,488	570,049	641,279
Weighted average units outstanding—diluted (in shares)									206,673,471	174,895,098	150,679,688
Income per share:
Basic (in dollars per share)	$ 0.15	$ 0.33	$ 0.32	$ 0.42	$ 0.26	$ (0.02)	$ 0.36	$ 0.42	$ 1.21	$ 0.99	$ 2.21
Diluted (in dollars per share)	$ 0.15	$ 0.33	$ 0.32	$ 0.42	$ 0.26	$ (0.02)	$ 0.36	$ 0.41	$ 1.21	$ 0.99	$ 2.20