Revenue - Disaggregation of Revenues By Performance Obligations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of revenue by performance obligation
Revenue	$ 653,481	$ 638,742	$ 1,927,237	$ 1,880,558
Management fee revenue - policy issuance and renewal services, net
Disaggregation of revenue by performance obligation
Revenue	484,551	474,427	1,412,096	1,385,923
Management fee revenue - policy issuance and renewal services, net | Transferred at point in time
Disaggregation of revenue by performance obligation
Revenue	484,551	474,427	1,412,096	1,385,923
Management fee revenue - administrative services, net
Disaggregation of revenue by performance obligation
Revenue	14,910	14,430	44,494	42,576
Management fee revenue - administrative services, net | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	14,910	14,430	44,494	42,576
Administrative services reimbursement revenue
Disaggregation of revenue by performance obligation
Revenue	147,710	142,730	451,229	431,305
Administrative services reimbursement revenue | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	147,710	142,730	451,229	431,305
Administrative services | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	$ 162,620	$ 157,160	$ 495,723	$ 473,881