Business Combinations - Acquisition Method for Recording Business Combinations (Detail)	6 Months Ended
	Jun. 30, 2022 USD ($)
Devitt Insurance Services Ltd [Member]
Business Acquisition [Line Items]
Cash Paid	$ 73,600,000
Accrued Liability	1,300,000
Escrow Deposited	3,400,000
Recorded Earnout Payable	12,500,000
Total Recorded Purchase Price	90,800,000
Maximum Potential Earnout Payable	12,500,000
Innovu Group Holding Company Limited [Member]
Business Acquisition [Line Items]
Cash Paid	85,400,000
Total Recorded Purchase Price	85,400,000
Twelve Other Acquisitions [Member]
Business Acquisition [Line Items]
Cash Paid	164,700,000
Accrued Liability	6,500,000
Escrow Deposited	9,100,000
Recorded Earnout Payable	35,500,000
Total Recorded Purchase Price	215,800,000
Maximum Potential Earnout Payable	79,200,000
2022 Acquisitions [Member]
Business Acquisition [Line Items]
Cash Paid	323,700,000
Accrued Liability	7,800,000
Escrow Deposited	12,500,000
Recorded Earnout Payable	48,000,000.0
Total Recorded Purchase Price	392,000,000.0
Maximum Potential Earnout Payable	$ 91,700,000