Consolidated Statement of Comprehensive Income (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
Other Comprehensive Income [Abstract]
Net income	$ 46,365	$ 47,888	$ 91,564	$ 95,276
Investment securities available for sale:
Net unrealized gains (losses)	35,557	(111,829)	56,184	(121,760)
Reclassification adjustment for net (gains) losses realized in net income	(34)	(34)	(412)	(334)
Income tax (expense) benefit	(13,655)	43,188	(21,441)	47,138
Other comprehensive income (loss) on investment securities available for sale	21,868	(68,675)	34,331	(74,956)
Defined benefit pension and postretirement obligations:
Amortization of prior service cost	15	17	30	35
Amortization of actuarial losses	316	1,073	632	2,145
Income tax (expense) benefit	(128)	(421)	(255)	(842)
Other comprehensive income on pension and postretirement obligations	203	669	407	1,338
Total other comprehensive income (loss)	22,071	(68,006)	34,738	(73,618)
Comprehensive income (loss)	$ 68,436	$ (20,118)	$ 126,302	$ 21,658