Income Taxes (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Income tax reconciliation computed at federal statutory rates to income tax expense
Provision for income taxes at statutory rate	$ 4,157,000	$ 3,119,000	$ 11,456,000	$ 9,045,000
Provision for income taxes at statutory rate, tax rate	35.00%	35.00%	35.00%	35.00%
State and local income taxes, net of federal tax benefit	181,000	110,000	468,000	318,000
State and local income taxes, net of federal tax benefit, tax rate	1.50%	1.20%	1.40%	1.20%
Stock compensation	79,000	51,000	213,000	179,000
Stock compensation, tax rate	0.70%	0.60%	0.70%	0.70%
Research credits		(88,000)		(231,000)
Research credits, tax rate		(1.00%)		(0.90%)
Effect of rate changes on deferred taxes	33,000		161,000	9,000
Effect of rate changes on deferred taxes, tax rate	0.30%		0.50%
Reversal of reserve for income taxes	(383,000)	(35,000)	(383,000)	(35,000)
Reversal of reserve for income taxes, tax rate	3.20%	(0.40%)	(1.20%)	0.10%
Disqualifying dispositions on incentive stock options	(42,000)	(40,000)	(121,000)	(135,000)
Disqualifying dispositions on incentive stock options, tax rate	(0.40%)	(0.50%)	(0.40%)	(0.50%)
Other, net	(139,000)	(197,000)	(188,000)	(337,000)
Other, net, tax rate	(1.20%)	(2.10%)	(0.50%)	(1.30%)
Reported income tax provision	3,886,000	2,920,000	11,606,000	8,813,000
Reported income tax provision, tax rate	32.70%	32.80%	35.50%	34.10%
Income Taxes (Textual) [Abstract]
Reserve for uncertain tax positions	$ 900,000		$ 900,000		$ 1,200,000