Cash and cash equivalents - Schedule of Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Abstract]
Cash	$ 3,726	$ 2,133
Cash equivalents	28,575	37,393
Cash and cash equivalents	$ 32,301	$ 39,526	$ 14,906	$ 11,006