Condensed Financial Information - Parent Company Only - Statement of Income (Details 1) (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
Statements of Income
Other-than-temporary impairment on equity securities									$ (13)	$ (16)	$ (62)
Net gain on sales of investment securities									305	1,417	432
Income before income taxes	6,434	7,612	6,168	6,209	6,609	6,646	5,715	4,688	26,423	23,658	19,038
Provision for federal and state income taxes, total	1,358	1,842	1,405	946	1,349	1,402	1,199	826	5,551	4,776	3,282
Equity in undistributed income of subsidiaries:
Net income	5,076	5,770	4,763	5,263	5,260	5,244	4,516	3,862	20,872	18,882	15,756
Parent Company [Member]
Statements of Income
Dividends from bank									20,482	12,482	12,482
Dividends from non-banks									1,200	1,190	1,190
Other-than-temporary impairment on equity securities									(13)	(16)	(62)
Net gain on sales of investment securities									70	58	105
Other income									17,463	14,986	15,976
Total operating income									39,202	28,700	29,691
Operating expenses									18,323	16,946	15,715
Income before income taxes									20,879	11,754	13,976
Provision for federal and state income taxes, total									(143)	(547)	73
Income before equity in undistributed income of subsidiaries									21,022	12,301	13,903
Equity in undistributed income of subsidiaries:
Bank									(140)	6,576	1,777
Non-banks									(10)	5	76
Net income									$ 20,872	$ 18,882	$ 15,756