Segment Reporting and Geographic Locations - Revenue and Long-Lived Assets for Each of Geographic Areas (Detail) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 189,485	$ 225,399	$ 243,190	$ 243,164	$ 223,602	$ 225,010	$ 233,391	$ 215,734	$ 486,354	$ 449,125	$ 711,753	$ 674,135	$ 901,238	$ 897,737	$ 755,231
Long-lived Assets	109,438				64,101								109,438	64,101	63,483
Right-of-use assets	792												792
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues													691,224	670,075	560,412
Long-lived Assets	70,870				49,874								70,870	49,874	49,060
Right-of-use assets	15,100												15,100
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues													48,070	51,451	44,013
Long-lived Assets	12,233				3,204								12,233	3,204	3,849
Right-of-use assets	9,300												9,300
All other countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues													161,944	176,211	150,806
Long-lived Assets	26,335				$ 11,023								26,335	$ 11,023	$ 10,574
Right-of-use assets	$ 11,300												$ 11,300