Goodwill and Intangible Assets, Net - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Goodwill	$ 51,889,000		$ 51,889,000		$ 51,889,000
Goodwill impairment amount			$ 0		$ 0
Weighted average remaining useful life			4 years
Amortization of intangible assets		$ 400,000	$ 100,000	$ 800,000
Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 100,000