Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income, Net of Tax (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Beginning Balance	$ 238,048	$ 247,734
Other comprehensive income (loss) before reclassifications	(18,306)	1,746
Amounts reclassified from accumulated other comprehensive income (loss)	(5,372)	(5,084)
Net other comprehensive income (loss) during period	(23,678)	(3,338)
Ending Balance	214,370	244,396
Securities Available For Sale [Member]
Beginning Balance	245,539	227,052
Other comprehensive income (loss) before reclassifications	(19,372)	1,224
Amounts reclassified from accumulated other comprehensive income (loss)	(3)	319
Net other comprehensive income (loss) during period	(19,375)	1,543
Ending Balance	226,164	228,595
Defined Benefit Plans [Member]
Beginning Balance	(49,071)	(42,958)
Other comprehensive income (loss) before reclassifications	1,066	799
Net other comprehensive income (loss) during period	1,066	799
Ending Balance	(48,005)	(42,159)
Derivatives [Member]
Beginning Balance	41,580	63,640
Other comprehensive income (loss) before reclassifications		(277)
Amounts reclassified from accumulated other comprehensive income (loss)	(5,369)	(5,403)
Net other comprehensive income (loss) during period	(5,369)	(5,680)
Ending Balance	$ 36,211	$ 57,960