Earnings per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Basic earnings per share:
Net income (loss)	$ (9,968)	$ (262,146)	$ 70,739	$ 67,239	$ 106,747	$ 84,050	$ 89,144	$ 69,304	$ (134,136)	$ 349,245	$ 284,373
Less preferred stock dividends	(5,481)	(5,481)	(5,480)	(5,480)	(5,481)	(2,070)	0	0	(21,922)	(7,551)
Net income (loss) available to common shareholders	(15,449)	(267,627)	65,259	61,759	101,266	81,980	89,144	69,304	(156,058)	341,694	284,373
Weighted average shares									98,337,362	93,185,520	71,708,058
Basic earnings (loss) per share	$ (0.16)	$ (2.72)	$ 0.66	$ 0.62	$ 1.02	$ 0.83	$ 0.91	$ 0.89	$ (1.59)	$ 3.67	$ 3.97
Diluted earnings per share:
Net income (loss)	(9,968)	(262,146)	70,739	67,239	106,747	84,050	89,144	69,304	(134,136)	349,245	284,373
Less preferred stock dividends	(5,481)	(5,481)	(5,480)	(5,480)	(5,481)	(2,070)	0	0	(21,922)	(7,551)
Net income (loss) available to common shareholders									$ (156,058)	$ 341,694	$ 284,373
Weighted average shares									98,337,362	93,185,520	71,708,058
Potential dilutive shares from exercise of stock options
Diluted weighted average shares									98,337,362	93,185,520	71,708,058
Diluted earnings (loss) per share	$ (0.16)	$ (2.72)	$ 0.66	$ 0.62	$ 1.02	$ 0.83	$ 0.91	$ 0.89	$ (1.59)	$ 3.67	$ 3.97