Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income, Net of Tax (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			$ 238,048	$ 247,734
Other comprehensive income (loss) before reclassifications			(76,250)	26,989
Amounts reclassified from accumulated other comprehensive income (loss)			(16,071)	0
Other comprehensive income (loss), net of tax	(9,875)	21,448	(92,321)	26,989
Ending Balance	145,727	274,723	145,727	274,723
Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			245,539	227,052
Other comprehensive income (loss) before reclassifications			(79,416)	41,010
Amounts reclassified from accumulated other comprehensive income (loss)			2	0
Other comprehensive income (loss), net of tax			(79,414)	41,010
Ending Balance	166,125	268,062	166,125	268,062
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			(49,071)	(42,958)
Other comprehensive income (loss) before reclassifications			3,197	2,655
Amounts reclassified from accumulated other comprehensive income (loss)			0	0
Other comprehensive income (loss), net of tax			3,197	2,655
Ending Balance	(45,874)	(40,303)	(45,874)	(40,303)
Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			41,580	63,640
Other comprehensive income (loss) before reclassifications			(31)	(16,676)
Amounts reclassified from accumulated other comprehensive income (loss)			(16,073)	0
Other comprehensive income (loss), net of tax			(16,104)	(16,676)
Ending Balance	$ 25,476	$ 46,964	$ 25,476	$ 46,964