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Business Combinations - Acquisition Method for Recording Business Combinations (Detail) shares in Thousands | 6 Months Ended
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Jun. 30, 2020 USD ($) shares
Business Acquisition [Line Items] |
Common Shares Issued | shares | 961
Common Shares Issued | $ 98,100,000
Cash Paid | 148,000,000.0
Accrued Liability | 1,800,000
Escrow Deposited | 9,000,000.0
Recorded Earnout Payable | 142,900,000
Total Recorded Purchase Price | 399,800,000
Maximum Potential Earnout Payable | $ 261,100,000
Capsicum Reinsurance Brokers LLP (CRB) [Member] |
Business Acquisition [Line Items] |
Common Shares Issued | shares | 584
Common Shares Issued | $ 62,900,000
Cash Paid | 64,500,000
Recorded Earnout Payable | 119,000,000.0
Total Recorded Purchase Price | 246,400,000
Maximum Potential Earnout Payable | 209,100,000
Hanover Excess and Surplus Inc and Hanover Finance Inc (HES) [Member] |
Business Acquisition [Line Items] |
Cash Paid | 30,100,000
Escrow Deposited | 3,000,000.0
Recorded Earnout Payable | 200,000
Total Recorded Purchase Price | 33,300,000
Maximum Potential Earnout Payable | $ 9,300,000
CRES Insurance Services, LLC [Member] |
Business Acquisition [Line Items] |
Common Shares Issued | shares | 288
Common Shares Issued | $ 28,500,000
Cash Paid | 1,500,000
Escrow Deposited | 1,000,000.0
Recorded Earnout Payable | 5,300,000
Total Recorded Purchase Price | 36,300,000
Maximum Potential Earnout Payable | $ 7,300,000
Nine Other Acquisitions [Member] |
Business Acquisition [Line Items] |
Common Shares Issued | shares | 89
Common Shares Issued | $ 6,700,000
Cash Paid | 51,900,000
Accrued Liability | 1,800,000
Escrow Deposited | 5,000,000.0
Recorded Earnout Payable | 18,400,000
Total Recorded Purchase Price | 83,800,000
Maximum Potential Earnout Payable | $ 35,400,000

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