Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Components of income from continuing operations before income taxes
US	$ 48,552,000	$ 40,122,000	$ 33,188,000
Foreign	(993,000)	1,200,000	2,222,000
Income from continuing operations before income taxes	47,559,000	41,322,000	35,410,000
Current:
Federal	12,845,000	8,857,000	4,776,000
State	1,653,000	1,005,000	939,000
Foreign	774,000	1,241,000	821,000
Deferred:
Federal	3,502,000	2,633,000	4,959,000
State	(576,000)	(276,000)	(320,000)
Foreign	(870,000)	(469,000)	(84,000)
Total	17,328,000	12,991,000	11,091,000
Reconciliation of statutory federal tax rate to effective income tax rate
Statutory federal rate (as a percent)	35.00%	35.00%	35.00%
State taxes (as a percent)	4.30%	3.80%	5.40%
Stock compensation relating to incentive stock options and employee stock purchase plans (as a percent)	0.60%	0.10%	(1.50%)
Research and other state tax credits (as a percent)	(2.80%)	(8.00%)	(9.10%)
Change in valuation allowance (as a percent)	(0.10%)	0.50%	(1.70%)
Change in state contingency reserve (as a percent)	(0.20%)	(0.40%)	1.00%
Foreign taxes (as a percent)	0.80%	0.60%	(0.10%)
Impact of state tax rate changes on net deferred tax assets (as a percent)	(0.20%)		1.30%
Other, net (as a percent)	(1.00%)	(0.20%)	1.00%
Effective income tax rate (as a percent)	36.40%	31.40%	31.30%
Undistributed earnings for certain non-US subsidiaries	$ 15,900,000