Comprehensive Income - Components of Comprehensive Income, Net of Related Tax (Parenthetical) (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
Components Of Comprehensive Income [Abstract]
Securities available for sale, Unrealized gains (losses) arising during the period, tax expense (benefit)	$ 2,937	$ (6,101)	$ 8,618	$ (6,200)
Securities available for sale, Reversal of non-credit related losses on debt securities not expected to be sold, tax expense			3,335
Securities available for sale, Reclassification adjustment for gains included in net income, tax expense	270	19	3,581	258
Unrealized gains (losses) on derivative instruments arising during the period, tax expense (benefit)	1,248	(2,080)	2,365	(2,453)
Unrealized gains on pension and postretirement benefit obligations arising during the period, tax expense	$ 117	$ 188	$ 234	$ 375