Revenue - Disaggregation of Revenues By Performance Obligations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of revenue by performance obligation
Revenue	$ 630,177	$ 616,737
Management fee revenue - policy issuance and renewal services, net
Disaggregation of revenue by performance obligation
Revenue	455,718	443,750
Management fee revenue - policy issuance and renewal services, net | Transferred at point in time
Disaggregation of revenue by performance obligation
Revenue	455,718	443,750
Management fee revenue - administrative services, net
Disaggregation of revenue by performance obligation
Revenue	14,847	14,771
Management fee revenue - administrative services, net | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	14,847	14,771
Administrative services reimbursement revenue
Disaggregation of revenue by performance obligation
Revenue	153,533	151,554
Administrative services reimbursement revenue | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	153,533	151,554
Administrative services | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	$ 168,380	$ 166,325