Segment Information - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) Segment	Mar. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | Segment	4
Total revenues	$ 619,280	$ 501,461
Document Period End Date	Mar. 31, 2019
London, Bermuda and Cayman Islands
Segment Reporting Information [Line Items]
Total revenues	$ 3,400	$ 3,300