Income taxes - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Taxes [Line Items]
Income tax provision (benefit)	$ (386,000)	$ 427,000	$ 91,000	$ 600,000
Goodwill generated from amortization of tax goodwill from acquisitions	82,000	233,000	166,000	296,000
Unrecognized tax benefits, period change			0
Interest and penalties related to uncertain tax positions			0
International Operations [Member]
Income Taxes [Line Items]
Foreign income tax expense	$ 252,000	$ 194,000	$ 839,000	$ 304,000