Revenue - Disaggregation of Revenues By Performance Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of revenue by performance obligation
Revenue	$ 2,840,124	$ 2,633,977	$ 2,536,489
Management fee revenue - policy issuance and renewal services
Disaggregation of revenue by performance obligation
Revenue	2,087,846	1,913,166	1,841,794
Management fee revenue - policy issuance and renewal services | Transferred at point in time
Disaggregation of revenue by performance obligation
Revenue	2,087,846	1,913,166	1,841,794
Administrative services | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	726,591	696,769	668,898
Management fee revenue - administrative services
Disaggregation of revenue by performance obligation
Revenue	58,323	58,286	59,463
Management fee revenue - administrative services | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	58,323	58,286	59,463
Administrative services reimbursement revenue
Disaggregation of revenue by performance obligation
Revenue	668,268	638,483	609,435
Administrative services reimbursement revenue | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	$ 668,268	$ 638,483	$ 609,435