Segment Reporting - Revenues Based on Location of Legal Entity (Detail) - USD ($) $ in Thousands	3 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	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues	$ 602,218	$ 593,106	$ 606,119	$ 551,274	$ 504,993	$ 513,012	$ 512,098	$ 497,774	$ 2,352,717	$ 2,027,877	$ 1,807,732
U.S.
Segment Reporting Information [Line Items]
Revenues									1,555,133	1,372,116	1,262,682
United Kingdom
Segment Reporting Information [Line Items]
Revenues									389,338	302,576	251,843
All other foreign countries
Segment Reporting Information [Line Items]
Revenues									$ 408,246	$ 353,185	$ 293,207