CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash Flows From Operating Activities:
Net income	$ 23,497	$ 23,303	$ 23,009
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	7,346	6,916	4,528
Net gains on sales of securities	(4,024)	(2,635)	(43)
Stock-based compensation expense	1,795	1,398	1,391
Provisions for loan losses	500	2,400	2,150
Deferred income tax expense	57	974	2,145
(Decrease) increase in income tax liability	(964)	1,073	(192)
Increase (decrease) in pension liability	2,822	(2,158)	(6,817)
Other operating activities, net	(2,323)	4,056	(528)
Net cash provided by operating activities	28,886	35,328	25,642
Cash Flows From Investing Activities:
Proceeds from sales of securities available-for-sale	95,742	69,747	5,930
Proceeds from maturities of securities available-for-sale	18,117	11,898	18,510
Purchase of securities available-for-sale	(104,351)	(114,646)	(61,768)
Net decrease (increase) in loans	34,378	(19,165)	35,981
Increase in payments in excess of funding	(14,128)	(2,144)	(27,769)
Purchases of premises and equipment, net	(4,857)	(3,099)	(1,925)
Environmental management acquisition		(7,798)
Net cash provided by (used in) investing activities	24,901	(65,207)	(31,041)
Cash Flows From Financing Activities:
Net (decrease) increase in noninterest-bearing demand deposits	(302)	12,187	18,859
Net increase in interest-bearing demand and savings deposits	32,645	21,683	36,956
Net decrease in time deposits	(13,555)	(18,530)	(26,037)
Net increase (decrease) in accounts and drafts payable	21,192	(72,440)	79,094
Cash dividends paid	(8,510)	(7,361)	(6,279)
Other financing activities, net	(1,083)	(534)	(161)
Net cash provided by (used in) financing activities	30,387	(64,995)	102,432
Net increase (decrease) in cash and cash equivalents	84,174	(94,874)	97,033
Cash and cash equivalents at beginning of year	141,088	235,962	138,929
Cash and cash equivalents at end of year	225,262	141,088	235,962
Supplemental information:
Cash paid for interest	2,855	3,196	4,424
Cash paid for income taxes	$ 8,265	$ 6,407	$ 6,287