Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Loss (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Reclassification Out Of Accumulated Other Comprehensive Loss [LineItems]
Amounts Reclassified from Accumulated Other Comprehensive Loss, before tax	$ (44,124)	$ (49,809)
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	12,814	15,278
Defined benefit pension plan:
Amortization of prior service cost	(202)
Amortization of net actuarial loss	(794)
Total before tax	(996)
Tax effect	418
Total net of tax	(578)
Total reclassifications, net of tax	578	441
Gains (losses) on securities transactions, net [Member]
Reclassification Out Of Accumulated Other Comprehensive Loss [LineItems]
Amounts Reclassified from Accumulated Other Comprehensive Loss, before tax	3,958
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	(1,659)
Amounts Reclassified from Accumulated Other Comprehensive Loss, net of tax	2,299
Interest and dividends on investment securities (taxable) [Member]
Reclassification Out Of Accumulated Other Comprehensive Loss [LineItems]
Amounts Reclassified from Accumulated Other Comprehensive Loss, before tax	113
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	(47)
Amounts Reclassified from Accumulated Other Comprehensive Loss, net of tax	66
Interest expense [Member]
Reclassification Out Of Accumulated Other Comprehensive Loss [LineItems]
Amounts Reclassified from Accumulated Other Comprehensive Loss, before tax	(1,880)
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	789
Amounts Reclassified from Accumulated Other Comprehensive Loss, net of tax	$ (1,091)