Goodwill and Intangible assets - Estimated Amortization Expense of Intangible Assets (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 1,400	$ 200	$ 3,300	$ 700
2017 (remaining three months)	1,398		1,398
2018	5,585		5,585
2019	4,036		4,036
2020	2,568		2,568
2021	2,433		2,433
2022	782		782
Thereafter	1,781		1,781
Total	$ 18,583		$ 18,583		$ 13,273