Consolidated Statements of Comprehensive Income (Loss) (unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 20,906	$ 26,510
Change in securities available-for-sale:
Unrealized holding gains (losses) for the period	18,306	12,055
Reclassification adjustment for securities gains realized in income	(2,683)	(559)
Other-than-temporary-impairment on available-for-sale securities associated with credit loss realized in income	0	100
Income tax effect	(5,796)	(4,463)
Unrealized gains on available-for-sale securities	9,827	7,133
Change in securities held-to-maturity:
Amortization of fair value for securities held-to-maturity previously recognized into accumulated other comprehensive income	337	397
Income tax effect	66	(127)
Changes from securities held-to-maturity	403	270
Cash flow hedges:
Net unrealized derivative gains (losses) on cash flow hedges	(5,628)	(1,937)
Reclassification adjustment for (gains) losses realized in net income	186
Income tax effect	2,068	737
Changes from cash flow hedges	(3,374)	(1,200)
Defined benefit pension plans:
Amortization of net loss recognized in income	738	352
Income tax effect	(281)	(19)
Changes from defined benefit pension plans	457	333
Other comprehensive income (loss), net of tax	7,313	6,536
Comprehensive income	$ 28,219	$ 33,046