Parent Company Only Financial Statements Condensed statements of income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Income before income taxes	$ 5,626	$ 5,851	$ 5,557	$ 5,401	$ 5,162	$ 4,250	$ 4,011	$ 4,478	$ 22,435	$ 17,901	$ 13,283
Income tax benefit	(2,117)	(2,204)	(2,078)	(2,011)	(1,892)	(1,571)	(1,433)	(1,633)	(8,410)	(6,529)	(4,522)
Net income	3,509	3,647	3,479	3,390	3,270	2,679	2,578	2,845	14,025	11,372	8,761
Comprehensive income									15,421	16,586	6,231
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Dividends from subsidiaries									1,438	938	6,744
Other income									64	40	8
Total income									1,502	978	6,752
Operating expenses									2,519	2,414	2,728
Income before income taxes									(1,017)	(1,436)	4,024
Income tax benefit									990	1,005	1,062
Income (loss) before equity in undistributed earnings of subsidiaries									(27)	(431)	5,086
Equity in undistributed earnings of subsidiaries									14,052	11,803	3,675
Net income									14,025	11,372	8,761
Comprehensive income									$ 15,421	$ 16,586	$ 6,231