Cash and cash equivalents - Schedule of Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Cash and Cash Equivalents [Abstract]
Cash	$ 18,686	$ 3,726
Cash equivalents	2,230	28,575
Cash and cash equivalents	$ 20,916	$ 32,301	$ 35,691	$ 39,526