Segment and Geographic Information - Summary of Revenue and Long-lived Assets (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenues	$ 184,795	$ 125,490	$ 353,773	$ 249,981
Long-lived assets	78,461		78,461		$ 71,795
United States [Member]
Segment Reporting Information [Line Items]
Revenues	157,727	104,141	299,337	207,756
Long-lived assets	63,915		63,915		62,356
United Kingdom [Member]
Segment Reporting Information [Line Items]
Revenues	22,086	20,706	44,505	40,973
Long-lived assets	14,527		14,527		9,410
Other [Member]
Segment Reporting Information [Line Items]
Revenues	4,982	$ 643	9,931	$ 1,252
Long-lived assets	$ 19		$ 19		$ 29