Debt Obligations and Credit Facilities - Amounts of Outstanding Debt and Accrued Interest (Details) - USD ($) $ in Thousands			3 Months Ended								12 Months Ended
	Dec. 27, 2018	Aug. 16, 2018	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
Line of Credit Facility [Line Items]
Carrying value of debt			$ 1,191,207				$ 861,539				$ 1,191,207	$ 861,539
Receipt of loans											1,070,502	1,132,507	$ 874,100
Repayment of loans											(742,574)	(914,319)	(912,140)
Interest expense on debt obligations											51,245	25,205	25,619
Amortization of debt issuance costs											953	537	416
Funds withheld balances and other											343	475	2,067
Total interest expense			13,519	$ 14,950	$ 13,036	$ 11,036	4,644	$ 4,640	$ 8,922	$ 8,011	52,541	26,217	$ 28,102
Senior Notes
Line of Credit Facility [Line Items]
Carrying value of debt			842,216				348,054				$ 842,216	348,054
Senior Notes | Senior Notes
Line of Credit Facility [Line Items]
Term											5 years
Carrying value of debt			348,616				348,054				$ 348,616	348,054
Senior Notes | Senior Notes Due 2029
Line of Credit Facility [Line Items]
Term											10 years
Carrying value of debt			493,600				0				$ 493,600	0
Loan facilities
Line of Credit Facility [Line Items]
Receipt of loans											1,070,500
Repayment of loans											$ (742,600)
Loan facilities | EGL Revolving Credit Facility
Line of Credit Facility [Line Items]
Term		5 years									5 years
Carrying value of debt			0				15,000				$ 0	15,000
Loan facilities | 2018 EGL Term Loan Facility
Line of Credit Facility [Line Items]
Term	3 years										3 years
Carrying value of debt			$ 348,991				$ 498,485				$ 348,991	$ 498,485
Repayment of loans											$ (150,000)