Comprehensive Income - Changes in AOCI, Net of Tax, by Component (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), balance at beginning of period			$ (51,133)
Other comprehensive income before reclassifications			26,571
Amounts reclassified from AOCI			(897)
Net current period other comprehensive income	$ 8,192	$ (8,973)	25,674	$ 2,050
Accumulated other comprehensive income (loss), balance at end of period	(25,459)		(25,459)
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			(3,873)
Other comprehensive income before reclassifications			21,085
Amounts reclassified from AOCI			(193)
Net current period other comprehensive income			20,892
Accumulated other comprehensive income (loss), balance at end of period	17,019		17,019
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			1,440
Other comprehensive income before reclassifications			4,693
Amounts reclassified from AOCI			(704)
Net current period other comprehensive income			3,989
Accumulated other comprehensive income (loss), balance at end of period	5,429		5,429
Unrecognized Pension and Postretirement Obligations [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), balance at beginning of period			(48,700)
Other comprehensive income before reclassifications			793
Net current period other comprehensive income			793
Accumulated other comprehensive income (loss), balance at end of period	$ (47,907)		$ (47,907)