Comprehensive Income - Changes in Accumulated Other Comprehensive Income, Net of Tax, by Component (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) [Line Items]
Accumulated other comprehensive income (loss), balance at beginning of period			$ (56,924)
Other comprehensive income (loss) before reclassifications			23,893
Amounts reclassified from accumulated other comprehensive income			(7,420)
Net current period other comprehensive income (loss)	(3,892)	(4,094)	16,473	(19,947)
Accumulated other comprehensive income (loss), balance at end of period	(40,451)		(40,451)
Unrealized Net Gains (Losses) on Securities Available for Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), balance at beginning of period			(11,874)
Other comprehensive income (loss) before reclassifications			13,120
Amounts reclassified from accumulated other comprehensive income			(7,420)
Net current period other comprehensive income (loss)			5,700
Accumulated other comprehensive income (loss), balance at end of period	(6,174)		(6,174)
Non-Credit Related Loss on Debt Securities not Expected to be Sold [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), balance at beginning of period			(6,192)
Other comprehensive income (loss) before reclassifications			6,192
Amounts reclassified from accumulated other comprehensive income
Net current period other comprehensive income (loss)			6,192
Accumulated other comprehensive income (loss), balance at end of period
Unrealized Losses on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), balance at beginning of period			(6,586)
Other comprehensive income (loss) before reclassifications			3,922
Amounts reclassified from accumulated other comprehensive income
Net current period other comprehensive income (loss)			3,922
Accumulated other comprehensive income (loss), balance at end of period	(2,664)		(2,664)
Unrecognized Pension and Postretirement Obligations [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), balance at beginning of period			(32,272)
Other comprehensive income (loss) before reclassifications			659
Amounts reclassified from accumulated other comprehensive income
Net current period other comprehensive income (loss)			659
Accumulated other comprehensive income (loss), balance at end of period	$ (31,613)		$ (31,613)