Revenue - Disaggregation of Revenues By Performance Obligations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of revenue by performance obligation
Revenue	$ 687,839	$ 653,481	$ 1,998,046	$ 1,927,237
Management fee revenue - policy issuance and renewal services
Disaggregation of revenue by performance obligation
Revenue	504,891	484,551	1,462,880	1,412,096
Management fee revenue - policy issuance and renewal services | Transferred at point in time
Disaggregation of revenue by performance obligation
Revenue	504,891	484,551	1,462,880	1,412,096
Administrative services | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	176,881	162,620	517,118	495,723
Management fee revenue - administrative services
Disaggregation of revenue by performance obligation
Revenue	14,471	14,910	43,985	44,494
Management fee revenue - administrative services | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	14,471	14,910	43,985	44,494
Administrative services reimbursement revenue
Disaggregation of revenue by performance obligation
Revenue	162,410	147,710	473,133	451,229
Administrative services reimbursement revenue | Transferred over time
Disaggregation of revenue by performance obligation
Revenue	$ 162,410	$ 147,710	$ 473,133	$ 451,229