Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Basic earnings per share:
Net income (loss)	$ 145,491	$ (83,892)	$ 24,556	$ (34,535)	$ (25,851)	$ 77,891	$ (12,477)	$ 16,798	$ 51,620	$ 56,361	$ (134,136)
Dividends declared on preferred stock									(21,922)	(21,922)	(21,922)
Net income (loss) available to common shareholders	$ 140,010	$ (89,372)	$ 19,076	$ (40,016)	$ (31,332)	$ 72,411	$ (17,958)	$ 11,318	$ 29,698	$ 34,439	$ (156,058)
Weighted average shares	96,546,219	96,545,913	96,790,541	96,783,199	96,728,821	96,563,132	96,515,599	96,606,081	96,665,489	96,603,634	98,337,362
Basic earnings (loss) per share	$ 1.45	$ (0.93)	$ 0.20	$ (0.41)	$ (0.32)	$ 0.75	$ (0.19)	$ 0.12	$ 0.31	$ 0.36	$ (1.59)
Diluted earnings per share:
Net income (loss)	$ 145,491	$ (83,892)	$ 24,556	$ (34,535)	$ (25,851)	$ 77,891	$ (12,477)	$ 16,798	$ 51,620	$ 56,361	$ (134,136)
Dividends declared on preferred stock									(21,922)	(21,922)	(21,922)
Net income (loss) available to common shareholders									$ 29,698	$ 34,439	$ (156,058)
Weighted average shares	96,546,219	96,545,913	96,790,541	96,783,199	96,728,821	96,563,132	96,515,599	96,606,081	96,665,489	96,603,634	98,337,362
Diluted weighted average shares	96,546,219	96,545,913	96,790,541	96,783,199	96,728,821	96,563,132	96,515,599	96,606,081	96,665,489	96,603,634	98,337,362
Diluted earnings (loss) per share	$ 1.45	$ (0.93)	$ 0.20	$ (0.41)	$ (0.32)	$ 0.75	$ (0.19)	$ 0.12	$ 0.31	$ 0.36	$ (1.59)