Goodwill and Intangible Assets, Net - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill	$ 53,132,000		$ 53,132,000		$ 31,328,000
Impairment of goodwill			0		$ 0
Amortization expense for intangible assets	$ 1,900,000	$ 900,000	$ 4,500,000	$ 2,400,000