Other Comprehensive Income (Loss) (Components of Accumulated Other Comprehensive Income, Net of Tax) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 29	$ (4,851)
Current period change in other comprehensive income (loss)	3,706	3,878
Ending balance	3,735	(973)
Unrealized gains and losses on securities available for sale:
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	7,743	(2,799)
Current period change in other comprehensive income (loss)	3,710	3,926
Ending balance	11,453	1,127
Amortization related to post-retirement obligations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(7,714)	(2,052)
Current period change in other comprehensive income (loss)	(4)	(48)
Ending balance	$ (7,718)	$ (2,100)