Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 100,920	$ 91,675	$ 72,460
Change in securities available-for-sale:
Unrealized holding gains for the period	(125,761)	37,178	43,221
Reclassification for securities transferred to held-to-maturity	31,005
Reclassification adjustment for securities gains realized in income	(4,341)	(15,052)	(8,691)
Other-than-temporary-impairment on available-for-sale debt securities recorded in other comprehensive income			(1,843)
Other-than-temporary-impairment on available-for-sale debt securities associated with credit loss realized in income	1,000	1,414	1,409
Income tax effect	37,935	(9,099)	(13,273)
Unrealized gains on available-for-sale securities	(60,162)	14,441	20,823
Change in securities held-to-maturity:
Adjustment for securities transferred to available-for-sale		(1,588)
Adjustment for securities transferred from available-for-sale	(31,005)
Amortization of fair value for securities held-to-maturity previously recognized into accumulated other comprehensive income	225	(870)	(1,535)
Income tax effect	10,744	982	613
Changes from securities held-to-maturity	(20,036)	(1,476)	(922)
Cash flow hedges:
Net unrealized derivative gains (losses) on cash flow hedges	(306)	(240)	(1,387)
Reclassification adjustment on cash flow hedges			216
Income tax effect	116	96	470
Changes from cash flow hedges	(190)	(144)	(701)
Defined benefit pension plans:
Net loss, settlement cost and amortization of net (gain) loss recognized in income	10,337	3,294	(4,878)
Income tax effect	(4,216)	(1,318)	1,951
Changes from defined benefit pension plans	6,121	1,976	(2,927)
Net current-period other comprehensive income (loss)	(74,267)	14,797	16,273
Comprehensive income	$ 26,653	$ 106,472	$ 88,733