Contracts with Customers - Summary of Expected Revenue Related to Performance Obligations (Detail) $ in Millions	Dec. 31, 2023 USD ($)
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 706.2
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 541.1
Remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2025-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 99.8
Remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2026-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 30.0
Remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2027-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 15.6
Remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2028-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 8.4
Remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2029-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 11.3
Remaining performance obligation, expected timing of satisfaction, period
Brokerage [Member]
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 533.6
Brokerage [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 498.4
Remaining performance obligation, expected timing of satisfaction, period	1 year
Brokerage [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2025-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 31.3
Remaining performance obligation, expected timing of satisfaction, period	1 year
Brokerage [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2026-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 1.9
Remaining performance obligation, expected timing of satisfaction, period	1 year
Brokerage [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2027-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 1.0
Remaining performance obligation, expected timing of satisfaction, period	1 year
Brokerage [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2028-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 0.5
Remaining performance obligation, expected timing of satisfaction, period	1 year
Brokerage [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2029-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 0.5
Remaining performance obligation, expected timing of satisfaction, period
Risk Management [Member]
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 172.6
Risk Management [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 42.7
Remaining performance obligation, expected timing of satisfaction, period	1 year
Risk Management [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2025-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 68.5
Remaining performance obligation, expected timing of satisfaction, period	1 year
Risk Management [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2026-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 28.1
Remaining performance obligation, expected timing of satisfaction, period	1 year
Risk Management [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2027-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 14.6
Remaining performance obligation, expected timing of satisfaction, period	1 year
Risk Management [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2028-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 7.9
Remaining performance obligation, expected timing of satisfaction, period	1 year
Risk Management [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2029-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Expected revenue related to performance obligations	$ 10.8
Remaining performance obligation, expected timing of satisfaction, period