Income Taxes - Components of Deferred Tax Assets and Liabilities (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets:
Loan and lease loss	$ 8,753	$ 10,559
Deferred compensation	2,613	2,539
Actuarial adjustments on postretirement benefits	7,551	6,717
Interest on nonaccrual loans	1,839	1,073
State net operating losses	1,441	987
Other-than-temporary impairments on equity securities	1,218	1,259
Alternative minimum tax credits	1,590
Gross deferred tax assets	25,005	23,134
Valuation allowance	(1,432)	(1,392)
Total deferred tax asset, net of valuation allowance	23,573	21,742
Deferred tax liabilities:
Market discount	1,624	1,337
Retirement plans	5,100	2,183
Intangible assets	1,567	1,100
Net unrealized holding gains on securities available for sale and swaps*	3,825	3,432
Other	60	111
Total deferred tax liabilities	12,176	8,163
Net deferred tax assets	$ 11,397	$ 13,579