Comprehensive Income - Components of Comprehensive Income, Net of Related Tax (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Components Of Comprehensive Income [Abstract]
Net income	$ 34,524	$ 28,538
Securities available for sale, Unrealized gains (losses) arising during the period, net of tax expense (benefit) of $5,681 and $(99)	10,550	(184)
Securities available for sale, Reversal of non-credit related losses on debt securities not expected to be sold, net of tax expense of $3,335	6,192
Securities available for sale, Reclassification adjustment for gains included in net income, net of tax expense of $3,311 and $239	(6,150)	(445)
Unrealized gains (losses) on derivative instruments arising during the period, net of tax expense (benefit) of $1,117 and $(373)	2,074	(694)
Unrealized gains on pension and postretirement benefit obligations arising during the period, net of tax expense of $117 and $188	217	349
Other comprehensive income (loss)	12,883	(974)
Comprehensive income	$ 47,407	$ 27,564