Revenue - Disaggregation of Revenues By Performance Obligations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of revenue by performance obligation
Revenue	$ 680,030	$ 657,019	$ 1,310,207	$ 1,273,756
Management fee revenue - policy issuance and renewal services
Disaggregation of revenue by performance obligation
Revenue	502,271	483,795	957,989	927,545
Management fee revenue - policy issuance and renewal services | Transferred at point in time
Disaggregation of revenue by performance obligation
Revenue	502,271	483,795	957,989	927,545
Administrative services | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	171,857	166,778	340,237	333,103
Management fee revenue - administrative services
Disaggregation of revenue by performance obligation
Revenue	14,667	14,813	29,514	29,584
Management fee revenue - administrative services | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	14,667	14,813	29,514	29,584
Administrative services reimbursement revenue
Disaggregation of revenue by performance obligation
Revenue	157,190	151,965	310,723	303,519
Administrative services reimbursement revenue | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	$ 157,190	$ 151,965	$ 310,723	$ 303,519