Income taxes - Additional Information (Detail) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)
Income Tax Disclosure [Abstract]
Income tax benefit	$ 226	$ 371
Other comprehensive loss unrealized holding gain on securities arising during period tax	200	900
Accrued income tax provision	$ 500	$ 500