Condensed Financial Statements of Parent Company (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Assets
Cash due from subsidiaries	$ 14,783	$ 11,897
Securities available for sale	191,504	174,918
Other assets	6,346	6,454
Total assets	1,104,361	1,067,102
Liabilities and Stockholders' Equity
Other liabilities	7,347	6,264
Stockholders' equity	150,109	141,299	129,187	122,076
Total liabilities and stockholders' equity	1,104,361	1,067,102
NBI [Member]
Assets
Cash due from subsidiaries	21	2
Securities available for sale	1,597	2,140
Investments in subsidiaries, at equity	148,443	139,267
Refundable income taxes	77	0
Other assets	635	570
Total assets	150,773	141,979
Liabilities and Stockholders' Equity
Other liabilities	664	680
Stockholders' equity	150,109	141,299
Total liabilities and stockholders' equity	$ 150,773	$ 141,979