Commitments and Contingencies - Operating Leases - Additional Information (Detail) $ in Thousands						1 Months Ended					12 Months Ended
	Feb. 28, 2019 ft²	Oct. 02, 2018 ft²	Sep. 30, 2018 ft²	Aug. 01, 2018 ft²	Jan. 01, 2018 ft²	Mar. 31, 2019 ft²	Dec. 31, 2018 ft²	Oct. 31, 2018 ft²	May 31, 2018 ft²	Apr. 30, 2018 ft²	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2019 USD ($)
Commitments And Contingencies [Line Items]
Lease expire date											Jan. 31, 2022
Operating lease option to extend											true
Operating lease renewal term											5 years
Right-of-use operating asset | $											$ 33,771			$ 5,300
Lessee, operating lease contract term											3 years
Rent expense | $											$ 10,200	$ 6,500	$ 3,700
Operating Lease One [Member]
Commitments And Contingencies [Line Items]
Office space rent under operating lease	58,442		54,943		54,943	63,017		58,442
Lease expire date					Aug. 15, 2024	Aug. 31, 2024		Aug. 31, 2024
Increased office space rent						4,575		3,499
Operating Lease Two [Member]
Commitments And Contingencies [Line Items]
Office space rent under operating lease					19,805					40,419
Lease expire date					Feb. 28, 2022					Aug. 31, 2024
Increased office space rent		7,133		13,481						20,614
Operating Lease Three [Member]
Commitments And Contingencies [Line Items]
Office space rent under operating lease									15,525
Lease expire date									Nov. 30, 2024
Operating Lease Five [Member]
Commitments And Contingencies [Line Items]
Office space rent under operating lease							15,975
Lease expire date							Feb. 29, 2024
Minimum [Member]
Commitments And Contingencies [Line Items]
Operating lease remaining lease terms											1 year
Maximum [Member]
Commitments And Contingencies [Line Items]
Operating lease remaining lease terms											6 years