Parent Company Financial Statements (Balance Sheet) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets:
Interest-bearing balances due from banks	$ 42,700	$ 51,800
Other assets	54,987	50,696
Total assets	3,586,874	3,188,867	3,071,884
Liabilities:
Junior subordinated debentures	22,681	22,681
Other liabilities	56,799	43,137
Total liabilities	3,240,595	2,859,221
Shareholders’ Equity:
Common stock of $.0625 par value; authorized 30,000,000 shares; issued and outstanding 16,746,363 shares in 2014 and 16,613,561 shares in 2013	1,047	1,038
Paid-in capital	101,204	97,566
Retained earnings	252,837	232,595
Accumulated other comprehensive loss	(8,809)	(1,553)	(10,499)	(1,895)
Total shareholders’ equity	346,279	329,646	295,652	281,351
Total liabilities and shareholders’ equity	3,586,874	3,188,867
Common stock, par value (in dollars per share)	$ 0.0625	$ 0.0625
Common stock, shares authorized (in shares)	30,000,000	30,000,000
Common stock, shares issued (in shares)	16,746,363	16,613,561
Common stock, shares outstanding (in shares)	16,746,363	16,613,561
Parent Company [Member]
Assets:
Cash on deposit with bank subsidiary	2,998	2,126
Interest-bearing balances due from banks	939	1,569
Investment in subsidiaries at equity value	365,766	349,342
Dividends receivable from subsidiaries	5,101	4,606
Other assets	311	494
Total assets	375,115	358,137
Liabilities:
Junior subordinated debentures	22,681	22,681
Dividends payable	5,617	4,756
Other liabilities	538	1,054
Total liabilities	28,836	28,491
Shareholders’ Equity:
Common stock of $.0625 par value; authorized 30,000,000 shares; issued and outstanding 16,746,363 shares in 2014 and 16,613,561 shares in 2013	1,047	1,038
Paid-in capital	101,204	97,566
Retained earnings	252,837	232,595
Accumulated other comprehensive loss	(8,809)	(1,553)
Total shareholders’ equity	346,279	329,646
Total liabilities and shareholders’ equity	$ 375,115	$ 358,137