Comprehensive Income - Changes in AOCI, Net of Tax, by Component (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 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	11,543
Amounts reclassified from AOCI	(520)
Net current period other comprehensive income	11,023	12,883
Accumulated other comprehensive income (loss), balance at end of period	(34,980)
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	8,400
Amounts reclassified from AOCI	6
Net current period other comprehensive income	8,406
Accumulated other comprehensive income (loss), balance at end of period	7,966
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	2,793
Amounts reclassified from AOCI	(526)
Net current period other comprehensive income	2,267
Accumulated other comprehensive income (loss), balance at end of period	2,124
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	350
Net current period other comprehensive income	350
Accumulated other comprehensive income (loss), balance at end of period	$ (45,070)