Comprehensive Income - Changes in AOCI, Net of Tax, by Component (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), balance at beginning of period			$ (46,003)
Other comprehensive income before reclassifications			3,108
Amounts reclassified from AOCI			(1,058)
Net current period other comprehensive income	$ (8,973)	$ 7,482	2,050	$ 20,365
Accumulated other comprehensive income (loss), balance at end of period	(43,953)		(43,953)
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			(440)
Other comprehensive income before reclassifications			1,212
Amounts reclassified from AOCI			(3)
Net current period other comprehensive income			1,209
Accumulated other comprehensive income (loss), balance at end of period	769		769
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			(143)
Other comprehensive income before reclassifications			1,196
Amounts reclassified from AOCI			(1,055)
Net current period other comprehensive income			141
Accumulated other comprehensive income (loss), balance at end of period	(2)		(2)
Unrecognized Pension and Postretirement Obligations [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), balance at beginning of period			(45,420)
Other comprehensive income before reclassifications			700
Net current period other comprehensive income			700
Accumulated other comprehensive income (loss), balance at end of period	$ (44,720)		$ (44,720)