Consolidated Statement of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other Comprehensive Income [Abstract]
Net income	$ 188,692	$ 178,973	$ 139,699
Investment securities available for sale:
Net unrealized gains (losses)	(158,207)	(19,042)	71,606
Reclassification adjustment for net (gains) losses realized in net income	(564)	(4,261)	1,112
Income tax (expense) benefit	61,266	9,651	(28,566)
Other comprehensive income (loss) on investment securities available for sale	(97,505)	(13,652)	44,152
Defined benefit pension and postretirement obligations:
Prior service cost, net of amortization	72	242	467
Net gain (loss), net of amortization	40,148	(6,941)	(14,810)
Income tax (expense) benefit	(15,562)	2,366	5,674
Other comprehensive income (loss) on pension and postretirement obligations	24,658	(4,333)	(8,669)
Derivatives used in cash flow hedging relationships:
Net unrealized gains (losses)	0	6	(557)
Reclassification adjustment for net losses and interest expense for interest differential on derivatives realized in net income	0	1,954	4,708
Income tax expense	0	(974)	(1,658)
Other comprehensive income on cash flow hedging relationships	0	986	2,493
Total other comprehensive income (loss)	(72,847)	(16,999)	37,976
Comprehensive income	$ 115,845	$ 161,974	$ 177,675