Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Contingencies And Commitments [Line Items]
Rent expenses	$ 12,400,000	$ 7,600,000	$ 7,200,000
Amount accrued for estimation of loss	0
Minimum
Contingencies And Commitments [Line Items]
Possible loss estimated	0
Maximum
Contingencies And Commitments [Line Items]
Possible loss estimated	$ 6,000,000