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, 2009	$ 754,623	$ 56,203	$ 422,225	$ (5,679)	$ (30,456)	$ 312,330
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	33,895	0	0	0	0	33,895
Other Comprehensive Income, Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	234,529	0	0	0	234,529	0
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest, Available-for-sale Securities	(2,302)	0	0	0	(2,302)	0
Other comprehensive income	266,122
Conversion of subordinated debentures	56	7	49	0	0	0
Acquisition of common stock	(50)	(6)	(44)	0	0	0
Allocation of common stock by ESOP, including excess income tax benefits	453	0	(31)	484	0	0
Share-based compensation, including excess income tax benefits	6,800	0	6,800	0	0	0
Issuance of common stock under compensation plans, including excess income tax benefits	2,785	489	2,296	0	0	0
Stockholders' Equity, Other	15,600	0	15,600	0	0	0
Stockholders' equity at end of period at Sep. 30, 2010	1,046,389	56,693	446,895	(5,195)	201,771	346,225
Stockholders' equity at beginning of period at Dec. 31, 2010	938,047	56,968	454,454	(4,815)	81,820	349,620
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	36,549	0	0	0	0	36,549
Other Comprehensive Income, Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	370,694	0	0	0	370,694	0
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest, Available-for-sale Securities	2,196	0	0	0	2,196	0
Other comprehensive income	409,439
Conversion of subordinated debentures	0
Acquisition of common stock	(13)	(1)	(12)	0	0	0
Allocation of common stock by ESOP, including excess income tax benefits	915	0	65	850	0	0
Share-based compensation, including excess income tax benefits	6,575	0	6,575	0	0	0
Issuance of common stock under compensation plans, including excess income tax benefits	4,574	888	3,686	0	0	0
Stockholders' equity at end of period at Sep. 30, 2011	$ 1,359,537	$ 57,855	$ 464,768	$ (3,965)	$ 454,710	$ 386,169