Revenue - Disaggregation of Revenues By Performance Obligations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of revenue by performance obligation
Revenue	$ 657,019	$ 647,710	$ 1,273,756	$ 1,241,816
Management fee revenue - policy issuance and renewal services, net
Disaggregation of revenue by performance obligation
Revenue	483,795	480,513	927,545	911,496
Management fee revenue - policy issuance and renewal services, net | Transferred at point in time
Disaggregation of revenue by performance obligation
Revenue	483,795	480,513	927,545	911,496
Management fee revenue - administrative services, net
Disaggregation of revenue by performance obligation
Revenue	14,813	14,195	29,584	28,146
Management fee revenue - administrative services, net | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	14,813	14,195	29,584	28,146
Administrative services reimbursement revenue
Disaggregation of revenue by performance obligation
Revenue	151,965	146,095	303,519	288,575
Administrative services reimbursement revenue | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	151,965	146,095	303,519	288,575
Administrative services | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	$ 166,778	$ 160,290	$ 333,103	$ 316,721