Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income, Net of Tax (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ 238,048	$ 247,734
Other comprehensive income (loss) before reclassifications			(71,712)	16,261
Amounts reclassified from accumulated other comprehensive income (loss)			(10,734)	(10,720)
Other comprehensive income (loss), net of tax	(58,768)	8,879	(82,446)	5,541
Ending Balance	155,602	253,275	155,602	253,275
Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			245,539	227,052
Other comprehensive income (loss) before reclassifications			(73,822)	14,852
Amounts reclassified from accumulated other comprehensive income (loss)			(7)	79
Other comprehensive income (loss), net of tax			(73,829)	14,931
Ending Balance	171,710	241,983	171,710	241,983
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(49,071)	(42,958)
Other comprehensive income (loss) before reclassifications			2,131	1,727
Other comprehensive income (loss), net of tax			2,131	1,727
Ending Balance	(46,940)	(41,231)	(46,940)	(41,231)
Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			41,580	63,640
Other comprehensive income (loss) before reclassifications			(21)	(318)
Amounts reclassified from accumulated other comprehensive income (loss)			(10,727)	(10,799)
Other comprehensive income (loss), net of tax			(10,748)	(11,117)
Ending Balance	$ 30,832	$ 52,523	$ 30,832	$ 52,523