Consolidated Statement of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Other Comprehensive Income [Abstract]
Net income	$ 47,388	$ 42,633
Investment securities available for sale:
Net unrealized gains (losses)	(9,931)	(1,914)
Reclassification adjustment for net (gains) losses realized in net income	(300)	(40)
Income tax (expense) benefit	3,950	762
Other comprehensive income (loss) on investment securities available for sale	(6,281)	(1,192)
Defined benefit pension and postretirement obligations:
Prior service cost, net of amortization	17	60
Net loss, net of amortization	1,073	640
Income tax expense	(421)	(273)
Other comprehensive income on pension and postretirement obligations	669	427
Derivatives used in cash flow hedging relationships:
Net unrealized gains (losses)	0	10
Reclassification adjustment for net losses and interest expense for interest differential on derivatives realized in net income	0	731
Income tax expense	0	(300)
Other comprehensive income on cash flow hedging relationships	0	441
Total other comprehensive income (loss)	(5,612)	(324)
Comprehensive income	$ 41,776	$ 42,309