Cash and cash equivalents - Schedule of Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash and Cash Equivalents [Abstract]
Cash	$ 2,133	$ 8,351
Cash equivalents	37,393	6,555
Cash and cash equivalents	$ 39,526	$ 14,906	$ 11,006	$ 2,001