Condensed Financial Information - Parent Company Only - Schedule of Condensed Cash Flow Statement (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$ 22,231	$ 21,189	$ 20,872
Adjustments to reconcile net income to net cash provided by operating activities:
Other-than-temporary impairment on equity securities	0	0	13
Net gain on sales of investment securities	(635)	(3,389)	(305)
Loss on termination of interest rate swap	0	1,866	0
Bank owned life insurance income	(1,628)	(2,968)	(2,670)
Depreciation of premises and equipment	3,243	2,927	2,903
Stock-based compensation	1,141	978	1,267
Contributions to pension and other postretirement benefit plans	(254)	(2,243)	(8,215)
Decrease in other assets	(1,093)	(2,873)	8,065
(Decrease) increase in accrued interest payable and other liabilities	(587)	1,101	2,119
Net cash provided by operating activities	31,867	32,806	37,139
Cash flows from investing activities:
Proceeds from bank owned life insurance	0	3,540	2,415
Net cash (used in) provided by investing activities	(38,439)	21,595	(58,181)
Cash flows from financing activities:
Payment for repurchase of trust preferred securities	0	(20,619)	0
Purchases of treasury stock	(4,605)	(12,012)	(2,319)
Stock issued under dividend reinvestment and employee stock purchase plans and other employee benefit programs	2,462	2,422	2,515
Proceeds from exercise of stock options	310	0	0
Cash dividends paid	(12,996)	(10,029)	(16,755)
Net cash provided by (used in) financing activities	5,921	(120,154)	79,584
Net increase (decrease) in cash and due from financial institutions	(651)	(65,753)	58,542
Cash and due from banks at beginning of year	32,646	98,399	39,857
Cash and due from banks at end of period	31,995	32,646	98,399
Cash paid during the year for:
Interest	4,118	5,997	8,701
Income tax, net of refunds received	5,899	5,352	1,819
Parent Company [Member]
Cash flows from operating activities:
Net income	22,231	21,189	20,872
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed net (income) loss of subsidiaries	(8,913)	(3,923)	150
Other-than-temporary impairment on equity securities	0	0	13
Net gain on sales of investment securities	(306)	(644)	(70)
Loss on termination of interest rate swap	0	1,866	0
Bank owned life insurance income	(238)	(1,070)	(255)
Depreciation of premises and equipment	364	344	358
Stock-based compensation	1,141	978	1,267
Contributions to pension and other postretirement benefit plans	(254)	(2,243)	(8,215)
Decrease in other assets	714	671	6,270
(Decrease) increase in accrued interest payable and other liabilities	(639)	(2,426)	2,451
Net cash provided by operating activities	14,100	14,742	22,841
Cash flows from investing activities:
Proceeds from sales of securities	1,131	1,244	2,666
Liquidation of subsidiary, net of cash acquired	0	15,011	1,096
Proceeds from bank owned life insurance	0	772	178
Other, net	(281)	(713)	1,280
Net cash (used in) provided by investing activities	850	16,314	5,220
Cash flows from financing activities:
Repayment of long-term debt	0	(375)	(1,500)
Payment for repurchase of trust preferred securities	0	(20,619)	0
Purchases of treasury stock	(4,605)	(12,012)	(2,319)
Stock issued under dividend reinvestment and employee stock purchase plans and other employee benefit programs	2,462	2,422	2,515
Proceeds from exercise of stock options	310	0	0
Cash dividends paid	(12,996)	(10,029)	(16,755)
Net cash provided by (used in) financing activities	(14,829)	(40,613)	(18,059)
Net increase (decrease) in cash and due from financial institutions	121	(9,557)	10,002
Cash and due from banks at beginning of year	2,999	12,556	2,554
Cash and due from banks at end of period	3,120	2,999	12,556
Cash paid during the year for:
Interest	2	754	1,194
Income tax, net of refunds received	$ 5,300	$ 5,017	$ 1,180