Income Taxes - Income Tax Reconciliation Computed at Federal Statutory Rates to Income Tax Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Income Tax Disclosure [Abstract]
Provision for income taxes at statutory rate	$ 4,063	$ 4,042	$ 8,560	$ 7,299
State and local income taxes, net of federal tax benefit	178	159	369	287
Stock compensation	70	72	140	134
Research credits	(51)		(376)
Disqualifying dispositions on incentive stock options	(32)	(46)	(181)	(79)
Effect of rate changes on deferred taxes				128
Other, net	71	(94)	18	(49)
Reported income tax provision	$ 4,299	$ 4,133	$ 8,530	$ 7,720
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, tax rate	1.50%	1.40%	1.50%	1.40%
Stock compensation, tax rate	0.60%	0.60%	0.60%	0.60%
Research credits, tax rate	(0.40%)		(1.50%)
Disqualifying dispositions of incentive stock options, tax rate	(0.30%)	(0.40%)	(0.80%)	(0.40%)
Effect of rate changes on deferred taxes, tax rate				0.60%
Other, net, tax rate	0.60%	(0.80%)	0.10%	(0.20%)
Reported income tax provision, tax rate	37.00%	35.80%	34.90%	37.00%