Other Comprehensive Income - Schedule of Changes in Accumulated Other Comprehensive Loss After Tax (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accumulated Other Comprehensive Income [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Balance	$ (62,441)
Net change	11,532	(56,722)	14,097
Total Accumulated Other Comprehensive Income (Loss), Balance	(50,909)	(62,441)
Unrealized Gains and Losses on AFS Securities [Member]
Accumulated Other Comprehensive Income [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Balance	(3,231)	14,930	9,623
Net change	4,137	(18,161)	5,307
Total Accumulated Other Comprehensive Income (Loss), Balance	906	(3,231)	14,930
Non-credit Impairment Losses on Securities [Member]
Accumulated Other Comprehensive Income [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Balance	(16,566)	(1,543)	(7,612)
Net change	12,391	(15,023)	6,069
Total Accumulated Other Comprehensive Income (Loss), Balance	(4,175)	(16,566)	(1,543)
Unrealized Gains and Losses on Derivatives [Member]
Accumulated Other Comprehensive Income [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Balance	(13,085)	(708)	(2,716)
Net change	409	(12,377)	2,008
Total Accumulated Other Comprehensive Income (Loss), Balance	(12,676)	(13,085)	(708)
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Balance	(29,559)	(18,398)	(19,111)
Net change	(5,405)	(11,161)	713
Total Accumulated Other Comprehensive Income (Loss), Balance	(34,964)	(29,559)	(18,398)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Balance	(62,441)	(5,719)	(19,816)
Net change	11,532	(56,722)	14,097
Total Accumulated Other Comprehensive Income (Loss), Balance	$ (50,909)	$ (62,441)	$ (5,719)