Parent Company Financial Statements (Statement of Income) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income:
Total income	$ 155,910	$ 137,719	$ 125,664
Expenses:
Interest on junior subordinated debentures	1,570	1,568	1,989
Legal and professional fees	2,240	1,927	1,813
Income before income taxes	50,872	42,646	34,353
Income tax benefit	(15,798)	(12,922)	(10,302)
Net income	35,074	29,724	24,051
Parent Company [Member]
Income:
Dividends from subsidiaries	16,188	14,439	15,416
Other income	3	2	2
Total income	16,191	14,441	15,418
Expenses:
Interest on junior subordinated debentures	1,570	1,568	1,989
Legal and professional fees	127	118	135
Other	279	257	252
Total expenses	1,976	1,943	2,376
Income before income taxes	14,215	12,498	13,042
Income tax benefit	682	669	819
Income before equity in undistributed earnings of subsidiaries	14,897	13,167	13,861
Equity in undistributed earnings of subsidiaries	20,177	16,557	10,190
Net income	$ 35,074	$ 29,724	$ 24,051