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, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			$ 140,434	$ 238,048
Other comprehensive income (loss) before reclassifications			32,184	(71,712)
Amounts reclassified from accumulated other comprehensive income (loss)			(12,150)	(10,734)
Other comprehensive income (loss), net of tax	17,720	(58,768)	20,034	(82,446)
Ending Balance	160,468	155,602	160,468	155,602
Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			146,672	245,539
Other comprehensive income (loss) before reclassifications			31,311	(73,822)
Amounts reclassified from accumulated other comprehensive income (loss)			(2)	(7)
Other comprehensive income (loss), net of tax			31,309	(73,829)
Ending Balance	177,981	171,710	177,981	171,710
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			(26,131)	(49,071)
Other comprehensive income (loss) before reclassifications			873	2,131
Amounts reclassified from accumulated other comprehensive income (loss)			0	0
Other comprehensive income (loss), net of tax			873	2,131
Ending Balance	(25,258)	(46,940)	(25,258)	(46,940)
Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			19,893	41,580
Other comprehensive income (loss) before reclassifications			0	(21)
Amounts reclassified from accumulated other comprehensive income (loss)			(12,148)	(10,727)
Other comprehensive income (loss), net of tax			(12,148)	(10,748)
Ending Balance	$ 7,745	$ 30,832	$ 7,745	$ 30,832