Income Taxes - Income Tax Reconciliation Computed at Federal Statutory Rates to Income Tax Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Tax Disclosure [Abstract]
Provision for income taxes at statutory rate	$ 3,899	$ 3,885	$ 12,927	$ 12,445
State and local income taxes, net of federal tax benefit	205	209	686	578
Stock compensation	78	71	243	211
Research credits		(47)		(424)
Effect of rate changes on deferred taxes		17		17
Reversal of reserve for income taxes	(131)	(89)	(131)	(79)
Disqualifying dispositions on incentive stock options	(62)	(19)	(104)	(200)
Other, net	113	10	138	19
Reported income tax provision	$ 4,102	$ 4,037	$ 13,759	$ 12,567
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	1.80%	1.90%	1.90%	1.60%
Stock compensation, tax rate	0.70%	0.60%	0.70%	0.60%
Research credits, tax rate		(0.40%)		(1.20%)
Effect of rate changes on deferred taxes, tax rate		0.20%
Reversal of reserve for income taxes , tax rate	(1.20%)	(0.80%)	(0.40%)	(0.20%)
Disqualifying dispositions of incentive stock options, tax rate	(0.60%)	(0.20%)	(0.30%)	(0.60%)
Other, net, tax rate	1.10%	0.10%	0.30%	0.10%
Reported income tax provision, tax rate	36.80%	36.40%	37.20%	35.30%