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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			$ 140,434	$ 238,048
Other comprehensive income (loss) before reclassifications			33,088	(76,250)
Amounts reclassified from accumulated other comprehensive income (loss)			(18,246)	(16,071)
Other comprehensive income (loss), net of tax	(5,192)	(9,875)	14,842	(92,321)
Ending Balance	155,276	145,727	155,276	145,727
Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			146,672	245,539
Other comprehensive income (loss) before reclassifications			31,778	(79,416)
Amounts reclassified from accumulated other comprehensive income (loss)			(23)	2
Other comprehensive income (loss), net of tax			31,755	(79,414)
Ending Balance	178,427	166,125	178,427	166,125
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			(26,131)	(49,071)
Other comprehensive income (loss) before reclassifications			1,310	3,197
Amounts reclassified from accumulated other comprehensive income (loss)			0	0
Other comprehensive income (loss), net of tax			1,310	3,197
Ending Balance	(24,821)	(45,874)	(24,821)	(45,874)
Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			19,893	41,580
Other comprehensive income (loss) before reclassifications			0	(31)
Amounts reclassified from accumulated other comprehensive income (loss)			(18,223)	(16,073)
Other comprehensive income (loss), net of tax			(18,223)	(16,104)
Ending Balance	$ 1,670	$ 25,476	$ 1,670	$ 25,476