Income taxes - Tax Provision before Discrete Items Reconciled to Recorded Provision for Income Taxes (Detail) (USD $)	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 before discrete items	$ 2,400,000	$ 2,600,000	$ 4,300,000	$ 5,200,000
Interest related to unrecognized tax benefits	100,000	100,000	200,000	200,000
Provision related to reassessment of taxes resulting from the filing of prior year foreign tax returns			300,000
Benefit related to restructuring and other expenses	(100,000)	(300,000)	(700,000)	(600,000)
Benefit related to the 2012 U.S. federal research and development tax credit			(3.2)
Tax deductions related to ESPP dispositions	(100,000)	(100,000)	(300,000)	(400,000)
Benefit related to reversals of uncertain tax positions due to statute of limitation expirations	(300,000)	(300,000)	(300,000)	(300,000)
Provision for income taxes	$ 2,009,000	$ 2,049,000	$ 253,000	$ 4,067,000