Segment Information - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) Segment	Jun. 30, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | Segment			4
Total revenues	$ 575,219	$ 473,187	$ 1,194,499	$ 974,648
Document Period End Date			Jun. 30, 2019
London, Bermuda and Cayman Islands
Segment Reporting Information [Line Items]
Total revenues	$ 4,600	$ 4,200	$ 8,000	$ 7,500