Other Comprehensive Income - Changes in AOCI, Net of Tax, by Component (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), balance at beginning of period	$ (61,369)
Other comprehensive income before reclassifications	5,420
Amounts reclassified from AOCI	(1,020)
Net current period other comprehensive income	4,400	$ 17,482
Accumulated other comprehensive income (loss), balance at end of period	(56,969)
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	(18,222)
Other comprehensive income before reclassifications	6,032
Amounts reclassified from AOCI	(787)
Net current period other comprehensive income	5,245
Accumulated other comprehensive income (loss), balance at end of period	(12,977)
Unrealized Net Gains (Losses) on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), balance at beginning of period	5,254
Other comprehensive income before reclassifications	(1,022)
Amounts reclassified from AOCI	(233)
Net current period other comprehensive income	(1,255)
Accumulated other comprehensive income (loss), balance at end of period	3,999
Unrecognized Pension and Postretirement Obligations [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), balance at beginning of period	(48,401)
Other comprehensive income before reclassifications	410
Net current period other comprehensive income	410
Accumulated other comprehensive income (loss), balance at end of period	$ (47,991)