Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Unallocated Common Stock Held by ESOP [Member]	Accumulated Other Comprehensive Income [Member]	Retained Earnings [Member]
Stockholders' equity at beginning of period at Dec. 31, 2012	$ 1,720,237	$ 61,751	$ 496,715	$ (2,583)	$ 686,807	$ 477,547
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	253,283					253,283
Other comprehensive income (loss)	(640,611)				(640,611)
Allocation of common stock by ESOP, including excess income tax benefits	3,390		1,438	1,952
Share-based compensation, including excess income tax benefits	13,624		13,624
Issuance of common stock under compensation plans, including excess income tax benefits	32,735	3,295	29,440
Extinguishment of convertible senior notes, net of tax, including shares of common stock issued upon conversion	62,663	5,489	57,174
Warrants reclassified to embedded derivative liability to be settled in cash	(47,991)		(47,991)
Dividends on common stock	(12,643)					(12,643)
Stockholders' equity at end of period at Dec. 31, 2013	1,384,687	70,535	550,400	(631)	46,196	718,187
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	126,023					126,023
Other comprehensive income (loss)	675,205				675,205
Allocation of common stock by ESOP, including excess income tax benefits	1,352		721	631
Share-based compensation, including excess income tax benefits	7,705		7,705
Issuance of common stock under compensation plans, including excess income tax benefits	14,705	1,568	13,137
Extinguishment of convertible senior notes, net of tax, including shares of common stock issued upon conversion	(3,529)	3,959	(7,488)
Warrants reclassified to embedded derivative liability to be settled in cash	(51,257)		(51,257)
Dividends on common stock	(15,015)					(15,015)
Stockholders' equity at end of period at Dec. 31, 2014	2,139,876	76,062	513,218	0	721,401	829,195
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	219,830					219,830
Other comprehensive income (loss)	(519,738)				(519,738)
Share-based compensation, including excess income tax benefits	9,976		9,976
Issuance of common stock via public offering	104,479	4,300	100,179
Issuance of common stock under compensation plans, including excess income tax benefits	7,986	944	7,042
Issuance of common stock to settle warrants that have reached their expiration	0	48	(48)
Dividends on common stock	(17,874)					(17,874)
Stockholders' equity at end of period at Dec. 31, 2015	$ 1,944,535	$ 81,354	$ 630,367	$ 0	$ 201,663	$ 1,031,151