Consolidated Statement of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Other Comprehensive Income [Abstract]
Net income	$ 45,199	$ 47,388
Investment securities available for sale:
Net unrealized gains (losses)	20,627	(9,931)
Reclassification adjustment for net (gains) losses realized in net income	(378)	(300)
Income tax (expense) benefit	(7,786)	3,950
Other comprehensive income (loss) on investment securities available for sale	12,463	(6,281)
Defined benefit pension and postretirement obligations:
Amortization of prior service cost	15	17
Amortization of actuarial losses	316	1,073
Income tax (expense) benefit	(127)	(421)
Other comprehensive income on pension and postretirement obligations	204	669
Total other comprehensive income (loss)	12,667	(5,612)
Comprehensive income (loss)	$ 57,866	$ 41,776