Tax Effects on Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pre-Tax Amount
Net change in unrealized gains on securities available-for-sale	$ 11,825	$ (16,928)	$ 4,097
Net available-for-sale securities gains reclassified into earnings	(41)	(5)	(3,016)
Adjustment to funded status of employee benefit plans	(13,394)	18,299	(271)
Other Comprehensive Income/(Loss)	(1,610)	1,366	810
Tax (Expense) Benefit
Net change in unrealized gains on securities available-for-sale, Tax (Expense) Benefit	(4,139)	5,925	(1,434)
Net available-for-sale securities gains reclassified into earnings, Tax (Expense) Benefit	15	2	1,055
Adjustment to funded status of employee benefit plans, Tax (Expense) Benefit	4,595	(6,405)	95
Other Comprehensive (Loss) Income, Tax (Expense) Benefit	471	(478)	(284)
Net of Tax Amount
Net change in unrealized gains on securities available-for-sale, Net of Tax Amount	7,686	(11,003)	2,663
Net available-for-sale securities gains reclassified into earnings, Net of Tax Amount	(26)	(3)	(1,961)
Adjustment to funded status of employee benefit plans, Net of Tax Amount	(8,799)	11,894	(176)
Other Comprehensive Income (Loss), After Tax	$ (1,139)	$ 888	$ 526