Consolidated Statements of Comprehensive Income (Loss) (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 37,669	$ 29,134	$ 84,731	$ 74,417
Change in securities available-for-sale:
Unrealized holding gains (losses) for the period	14,509	5,772	6,581	29,274
Reclassification adjustment for securities gains realized in income	(861)	(2,713)	(4,056)	(4,961)
Other-than-temporary-impairment on available-for-sale securities associated with credit loss realized in income			0	100
Income tax effect	(5,021)	(1,222)	(1,101)	(9,312)
Unrealized gains on available-for-sale securities	8,627	1,837	1,424	15,101
Change in securities held-to-maturity:
Amortization of fair value for securities held-to-maturity previously recognized into accumulated other comprehensive income	455	395	1,222	1,017
Income tax effect	(155)	(126)	(236)	(311)
Changes from securities held-to-maturity	300	269	986	706
Cash flow hedges:
Net unrealized derivative gains (losses) on cash flow hedges	(10,278)	987	(12,349)	(4,134)
Reclassification adjustment for (gains) losses realized in net income	902	103	1,527	141
Income tax effect	3,563	(676)	4,112	1,256
Changes from cash flow hedges	(5,813)	414	(6,710)	(2,737)
Defined benefit pension plans:
Amortization of net loss recognized in income	917	329	2,380	1,272
Income tax effect	(349)	(125)	(905)	(493)
Changes from defined benefit pension plans	568	204	1,475	779
Other comprehensive income (loss), net of tax	3,682	2,724	(2,825)	13,849
Comprehensive income	$ 41,351	$ 31,858	$ 81,906	$ 88,266