Revenue - Disaggregation of Revenues By Performance Obligations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of revenue by performance obligation
Revenue	$ 616,737	$ 594,106
Management fee revenue - policy issuance and renewal services, net
Disaggregation of revenue by performance obligation
Revenue	443,750	430,983
Management fee revenue - policy issuance and renewal services, net | Transferred at point in time
Disaggregation of revenue by performance obligation
Revenue	443,750	430,983
Management fee revenue - administrative services, net
Disaggregation of revenue by performance obligation
Revenue	14,771	13,951
Management fee revenue - administrative services, net | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	14,771	13,951
Administrative services reimbursement revenue
Disaggregation of revenue by performance obligation
Revenue	151,554	142,480
Administrative services reimbursement revenue | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	151,554	142,480
Administrative services | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	$ 166,325	$ 156,431