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Business Combinations - Acquisition Method for Recording Business Combinations (Detail) shares in Thousands | 12 Months Ended
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Dec. 31, 2017 USD ($) shares
Business Acquisition [Line Items] |
Common Shares Issued | shares | 688
Common Share Value | $ 37,700,000
Cash Paid | 372,400,000
Accrued Liability | 0
Escrow Deposited | 34,600,000
Recorded Earnout Payable | 101,200,000
Total Recorded Purchase Price | 545,900,000
Maximum Potential Earnout Payable | 201,000,000
Construction Risk Solutions, LLC [Member] |
Business Acquisition [Line Items] |
Cash Paid | 27,900,000
Accrued Liability | 0
Escrow Deposited | 3,100,000
Recorded Earnout Payable | 4,400,000
Total Recorded Purchase Price | 35,400,000
Maximum Potential Earnout Payable | 10,000,000
Hill, Chesson And Woody [Member] |
Business Acquisition [Line Items] |
Cash Paid | 34,800,000
Accrued Liability | 0
Escrow Deposited | 700,000
Recorded Earnout Payable | 15,900,000
Total Recorded Purchase Price | 51,400,000
Maximum Potential Earnout Payable | 24,400,000
Presidio Group, Inc. [Member] |
Business Acquisition [Line Items] |
Cash Paid | 41,800,000
Accrued Liability | 0
Escrow Deposited | 4,800,000
Recorded Earnout Payable | 7,000,000
Total Recorded Purchase Price | 53,600,000
Maximum Potential Earnout Payable | 15,000,000
Commercial Insurance Brokers [Member] |
Business Acquisition [Line Items] |
Cash Paid | 17,700,000
Accrued Liability | 0
Escrow Deposited | 2,000,000
Recorded Earnout Payable | 800,000
Total Recorded Purchase Price | 20,500,000
Maximum Potential Earnout Payable | $ 3,600,000
Williams - Manny Insurance Group [Member] |
Business Acquisition [Line Items] |
Common Shares Issued | shares | 170
Common Share Value | $ 9,800,000
Cash Paid | 28,200,000
Accrued Liability | 0
Escrow Deposited | 2,000,000
Recorded Earnout Payable | 5,400,000
Total Recorded Purchase Price | 45,400,000
Maximum Potential Earnout Payable | 11,500,000
GPL Assurance Inc. (GPL) [Member] |
Business Acquisition [Line Items] |
Cash Paid | 37,800,000
Accrued Liability | 0
Escrow Deposited | 4,200,000
Recorded Earnout Payable | 5,800,000
Total Recorded Purchase Price | 47,800,000
Maximum Potential Earnout Payable | 8,000,000
Lutgert Insurance (LI) [Member] |
Business Acquisition [Line Items] |
Cash Paid | 25,200,000
Accrued Liability | 0
Escrow Deposited | 1,300,000
Recorded Earnout Payable | 6,400,000
Total Recorded Purchase Price | 32,900,000
Maximum Potential Earnout Payable | 10,200,000
DiBrina Group (DBG) [Member] |
Business Acquisition [Line Items] |
Cash Paid | 38,600,000
Accrued Liability | 0
Escrow Deposited | 4,500,000
Recorded Earnout Payable | 13,100,000
Total Recorded Purchase Price | 56,200,000
Maximum Potential Earnout Payable | $ 24,200,000
31 Other Acquisitions [Member] |
Business Acquisition [Line Items] |
Common Shares Issued | shares | 518
Common Share Value | $ 27,900,000
Cash Paid | 120,400,000
Accrued Liability | 0
Escrow Deposited | 12,000,000
Recorded Earnout Payable | 42,400,000
Total Recorded Purchase Price | 202,700,000
Maximum Potential Earnout Payable | $ 94,100,000

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