Consolidated Statements of Comprehensive Income (Loss) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 23,948	$ 19,737	$ 76,371	$ 68,666
Change in securities available-for-sale:
Unrealized holding gains (losses) for the period	(29,839)	23,002	(117,224)	40,463
Reclassification for securities transferred to held-to-maturity	31,005		31,005
Reclassification adjustment for securities gains realized in income	(186)	(2,877)	(2,994)	(10,488)
Other-than-temporary-impairment on available-for-sale securities associated with credit loss realized in income		202		1,078
Income tax effect	272	(7,901)	34,638	(12,076)
Unrealized gains on available-for-sale securities	1,252	12,426	(54,575)	18,977
Change in securities held-to-maturity:
Adjustment for securities transferred to available-for-sale		(1,588)		(1,588)
Fair value adjustment for securities transferred from available-for-sale	(31,005)		(31,005)
Amortization of fair value for securities held-to-maturity previously recognized into accumulated other comprehensive income	193	(232)	(161)	(693)
Income tax effect	10,725	729	10,866	913
Changes from securities held-to-maturity	(20,087)	(1,091)	(20,300)	(1,368)
Cash flow hedges:
Net unrealized derivative gains (losses) on cash flow hedges	(2,609)		(1,735)	(240)
Reclassification adjustment on cash flow hedges
Income tax effect	1,009	(1)	660	95
Changes from cash flow hedges	(1,600)	(1)	(1,075)	(145)
Defined benefit pension plans:
Amortization of net loss recognized in income	849	1,007	2,551	3,021
Income tax effect	(323)	(403)	(1,332)	(1,209)
Changes from defined benefit pension plans	526	604	1,219	1,812
Net current-period other comprehensive income (loss)	(19,909)	11,938	(74,731)	19,276
Comprehensive income (loss)	$ 4,039	$ 31,675	$ 1,640	$ 87,942