Condensed Financial Information Parent Company Only - Statement of Cash Flows (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities:
Net income	$ 20,872	$ 18,882	$ 15,756
Adjustments to reconcile net income to net cash provided by operating activities:
Other-than-temporary impairment on equity securities	13	16	62
Net gain on sales of investment securities	(305)	(1,417)	(432)
Depreciation of premises and equipment	2,925	2,591	2,517
Contributions to pension and other postretirement benefit plans	(8,215)	(2,325)	(2,139)
Stock-based compensation	1,267	888	1,045
Net cash provided by operating activities	37,139	42,698	34,846
Cash flows from investing activities:
Net cash provided by investing activities	(58,181)	(57,788)	(84,549)
Cash flows from financing activities:
Net decrease in short-term borrowings	(18,458)	(5,131)	(68,508)
Purchases of treasury stock	(2,319)	(1,928)	(153)
Stock issued under dividend reinvestment and employee stock purchase plans and other employee benefit programs	2,515	2,287	2,189
Cash dividends paid	(16,755)	(13,367)	(13,249)
Net cash provided by financing activities	79,584	43,323	40,792
Net increase (decrease) in cash and due from banks	58,542	28,233	(8,911)
Cash and due from banks at beginning of year	39,857	11,624	20,535
Cash and due from banks at end of year	98,399	39,857	11,624
Cash paid during the year for:
Interest	8,701	11,202	21,202
Income taxes, net of refunds received	1,819	4,626	2,730
Parent Company [Member]
Cash flows from operating activities:
Net income	20,872	18,882	15,756
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed net income of subsidiaries	150	(6,581)	(1,853)
Other-than-temporary impairment on equity securities	13	16	62
Net gain on sales of investment securities	(70)	(58)	(105)
Depreciation of premises and equipment	358	341	185
Contributions to pension and other postretirement benefit plans	(8,215)	(2,325)	(2,139)
Decrease (increase) in other assets	6,193	(1,728)	(2,736)
Increase in other liabilities	2,451	2,613	1,018
Net cash provided by operating activities	23,019	12,048	11,233
Cash flows from investing activities:
Proceeds from sales of securities	2,666	7,127	7,265
Purchases of investment securities		(2,525)	(7,000)
Liquidation of subsidiary, net of cash required	1,096		2,384
Other, net	1,280	(196)	147
Net cash provided by investing activities	5,042	4,406	2,796
Cash flows from financing activities:
Net decrease in short-term borrowings		(40)	(754)
Repayment of long-term debt	(1,500)	(1,500)	(1,500)
Purchases of treasury stock	(2,319)	(1,928)	(153)
Stock issued under dividend reinvestment and employee stock purchase plans and other employee benefit programs	2,515	2,287	2,189
Cash dividends paid	(16,755)	(13,367)	(13,249)
Net cash provided by financing activities	(18,059)	(14,548)	(13,467)
Net increase (decrease) in cash and due from banks	10,002	1,906	562
Cash and due from banks at beginning of year	2,554	648	86
Cash and due from banks at end of year	12,556	2,554	648
Cash paid during the year for:
Interest	1,194	1,211	1,250
Income taxes, net of refunds received	$ 1,786	$ 4,626	$ 2,501