Cash and cash equivalents - Schedule of Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Abstract]
Cash	$ 92,980	$ 8,351
Cash equivalents	16,393	6,555
Cash and cash equivalents	$ 109,373	$ 14,906	$ 15,869	$ 11,006