Business Combinations - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) Acquisition	Mar. 31, 2019 USD ($) Acquisition	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Business Acquisition [Line Items]
Number of acquisitions | Acquisition	5	8
Aggregate purchase price of acquisitions	$ 100
Payments to Acquire Businesses, Gross	153,291
Net assets acquired	168,816
Goodwill, Acquired During Period	135,482
Goodwill currently deductible for income tax purposes	121,500
Goodwill related to the recorded earn-out payables	14,000
Total revenues related to acquisitions	5,600
Income (loss) before income taxes related to acquisitions	500
Estimated acquisition earn-out payables	157,720	$ 108,710	$ 161,513	$ 89,924
Maximum Future Contingency payments Acquisitions	366,500
Other Noncurrent Liabilities
Business Acquisition [Line Items]
Estimated acquisition earn-out payables	145,300
Accounts payable
Business Acquisition [Line Items]
Estimated acquisition earn-out payables	12,400
Retail
Business Acquisition [Line Items]
Goodwill, Acquired During Period	657
National Programs
Business Acquisition [Line Items]
Goodwill, Acquired During Period	55,607
Wholesale Brokerage
Business Acquisition [Line Items]
Goodwill, Acquired During Period	79,110
Services
Business Acquisition [Line Items]
Goodwill, Acquired During Period	108
Goodwill adjusted amount	$ 100
Purchased Customer Accounts
Business Acquisition [Line Items]
Weighted average life (years)	15 years
Non-compete Agreements
Business Acquisition [Line Items]
Weighted average life (years)	5 years
Business Combinations - Asset Deals
Business Acquisition [Line Items]
Number of acquisitions | Acquisition	5
Other Acquisitions | Maximum
Business Acquisition [Line Items]
Net assets acquired	$ 10,000