Consolidated Statements of Changes in Stockholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Unallocated Common Stock Held by ESOP [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Stockholders' equity at beginning of period at Dec. 31, 2011	$ 1,408,679	$ 57,837	$ 468,281	$ (3,620)	$ 428,952	$ 457,229
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	10,471				10,471
Other comprehensive income	(48,482)					(48,482)
Conversion of subordinated debentures		7	49
Allocation of common stock by ESOP, including excess income tax benefits			22	333
Share-based compensation, including excess income tax benefits			1,774
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures		778	(47)
Stockholders' equity at end of period at Mar. 31, 2012	1,373,584	58,622	470,079	(3,287)	439,423	408,747
Stockholders' equity at beginning of period at Dec. 31, 2012	1,720,237	61,751	496,715	(2,583)	477,547	686,807
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	26,031				26,031
Other comprehensive income	(25,144)					(25,144)
Allocation of common stock by ESOP, including excess income tax benefits			58	317
Share-based compensation, including excess income tax benefits			1,488
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures		1,033	6,209
Stockholders' equity at end of period at Mar. 31, 2013	$ 1,730,229	$ 62,784	$ 504,470	$ (2,266)	$ 503,578	$ 661,663