CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 18,773	$ 28,478	$ 45,283	$ 52,423
Change in securities available-for-sale:
Unrealized holding gains (losses) for the period	11,447	(73,602)	23,502	(87,385)
Reclassification adjustment for securities gains realized in income	(1,689)	(1,789)	(2,248)	(2,808)
Other-than-temporary-impairment on available-for-sale securities associated with credit loss realized in income			100
Income tax effect	(3,627)	28,957	(8,090)	34,366
Unrealized gains on available-for-sale securities	6,131	(46,434)	13,264	(55,827)
Change in securities held-to-maturity:
Amortization of fair value for securities held-to-maturity previously recognized into accumulated other comprehensive income	225	(177)	622	(354)
Income tax effect	(58)	70	(185)	141
Changes from securities held-to-maturity	167	(107)	437	(213)
Cash flow hedges:
Net unrealized derivative gains (losses) on cash flow hedges	(3,146)	874	(5,083)	874
Income tax effect	1,195	(349)	1,932	(349)
Changes from cash flow hedges	(1,951)	525	(3,151)	525
Defined benefit pension plans:
Amortization of net loss recognized in income	591	842	943	1,702
Income tax effect	(349)	(665)	(368)	(1,009)
Changes from defined benefit pension plans	242	177	575	693
Other comprehensive income (loss), net of tax	4,589	(45,839)	11,125	(54,822)
Comprehensive income (loss)	$ 23,362	$ (17,361)	$ 56,408	$ (2,399)