Earnings per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								9 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net Income (Loss) Attributable to Parent									$ 74,835	$ 74,835	$ 200,352	$ 218,221
Numerator:
Net income attributable to common shareholders	$ 638	$ 1,821	$ 42,246	$ 21,758	$ 75,433	$ 41,174	$ 58,447	$ 25,298		66,463	200,352	218,221
Preferred Stock Dividends, Income Statement Impact										(8,372)	0	0
Less: Dividends paid on unvested restricted shares										(1,029)	(1,105)	(1,180)
Less: Undistributed earnings attributable to unvested restricted shares										0	(188)	(378)
Net income attributable to common shareholders excluding amounts attributable to unvested restricted shares										$ 65,434	$ 199,059	$ 216,663
Denominator:
Weighted-average number of common shares - basic (in shares)	174,147,522	140,249,961	123,785,735	123,734,173	123,698,633	123,621,323	123,544,034	123,739,823		140,616,838	123,651,003	128,444,469
Unvested restricted shares (in shares)										77,211	228,004	523,285
Unvested performance units (in shares)										0	0	0
Weighted-average number of common shares - diluted (in shares)	174,210,578	140,307,269	123,871,762	123,841,400	123,757,660	123,836,452	123,942,846	124,141,824		140,694,049	123,879,007	128,967,754
Net income per share attributable to common shareholders - basic (in dollars per share)	$ 0.00	$ 0.01	$ 0.34	$ 0.17	$ 0.61	$ 0.33	$ 0.47	$ 0.20		$ 0.47	$ 1.61	$ 1.69
Net income per share attributable to common shareholders - diluted (in dollars per share)	$ 0.00	$ 0.01	$ 0.34	$ 0.17	$ 0.61	$ 0.33	$ 0.47	$ 0.20		$ 0.47	$ 1.61	$ 1.68