Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Income tax reconciliation computed at federal statutory rates to income tax expense
Provision for income taxes at statutory rate	$ 4,497	$ 3,257
Provision for income taxes at statutory rate, tax rate	35.00%	35.00%
State and local income taxes, net of federal tax benefit	191	128
State and local income taxes, net of federal tax benefit, tax rate	1.50%	1.40%
Stock compensation	70	62
Stock compensation, tax rate	0.50%	0.60%
Research credits	(325)
Research credits, tax rate	(2.50%)
Disqualifying dispositions on incentive stock options	(148)	(33)
Disqualifying dispositions on incentive stock options, tax rate	(1.20%)	(0.30%)
Effect of rate changes on deferred taxes		128
Effect of rate changes on deferred taxes, tax rate		1.40%
Other, net	(54)	45
Other, net, tax rate	(0.40%)	0.40%
Reported income tax provision	$ 4,231	$ 3,587
Reported income tax provision, tax rate	32.90%	38.50%