Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017
Goodwill [Roll Forward]
Goodwill	$ 3,014
Acquisition of ICAR	6,852
Foreign currency effect on goodwill	146
Goodwill	10,012		$ 3,014
Amortization of intangible assets	$ 484	$ 144
Minimum
Goodwill [Roll Forward]
Estimated useful lives of intangible assets (in years)			2 years
Maximum
Goodwill [Roll Forward]
Estimated useful lives of intangible assets (in years)			6 years