Parent Company Financial Statements (Balance Sheet) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Assets:
Interest-bearing balances due from banks	$ 32,200	$ 41,600
Other assets	63,409	59,155
Total assets	3,071,884	3,064,098	2,909,525
Liabilities:
Junior subordinated debentures	32,991	32,991
Other liabilities	68,226	63,233
Total liabilities	2,776,232	2,782,747
Shareholders’ Equity:
Common stock of $.0625 par value; authorized 30,000,000 shares; issued and outstanding 16,379,771 shares in 2012 and 16,292,471 shares in 2011	1,024	1,018
Paid-in capital	91,453	88,030
Retained earnings	213,674	194,198
Accumulated other comprehensive loss	(10,499)	(1,895)	4,025	3,337
Total shareholders’ equity	295,652	281,351	268,864	254,946
Total liabilities and shareholders’ equity	3,071,884	3,064,098
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)	16,379,771	16,292,471
Common stock, shares outstanding (in shares)	16,379,771	16,292,471
Parent Company [Member]
Assets:
Cash on deposit with bank subsidiary	1,694	1,176
Interest-bearing balances due from banks	1,970	1,930
Investment in subsidiaries at equity value	325,717	311,946
Dividends receivable from subsidiaries	4,198	3,900
Other assets	891	968
Total assets	334,470	319,920
Liabilities:
Junior subordinated debentures	32,991	32,991
Dividends payable	4,152	3,688
Other liabilities	1,675	1,890
Total liabilities	38,818	38,569
Shareholders’ Equity:
Common stock of $.0625 par value; authorized 30,000,000 shares; issued and outstanding 16,379,771 shares in 2012 and 16,292,471 shares in 2011	1,024	1,018
Paid-in capital	91,453	88,030
Retained earnings	213,674	194,198
Accumulated other comprehensive loss	(10,499)	(1,895)
Total shareholders’ equity	295,652	281,351
Total liabilities and shareholders’ equity	$ 334,470	$ 319,920
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)	16,379,771	16,292,471
Common stock, shares outstanding (in shares)	16,379,771	16,292,471