Fair Value (Details)	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	$ 69,145,000	$ 73,649,000
Fair value, assets, Level 2 to Level 3 transfers, amount	0
Contingent payment arrangements	4,400,000		$ 17,384,000
Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent payment arrangements	29,723,000	22,911,000
Recurring | Contingent Payment Arrangements
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent payment arrangements	29,700,000	22,900,000
Software publishing company
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	2,000,000.0	1,000,000.0
Start-up company
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	0	900,000
Equity method investee
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	2,500,000	2,900,000
Broker dealer exchange memberships
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	$ 3,300,000	$ 3,200,000
Revenue growth rate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Acquisition-related contingent liability		0.007
Revenue growth rate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Acquisition-related contingent liability		0.500
Revenue growth rate | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Acquisition-related contingent liability		0.049
Discount rate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Acquisition-related contingent liability		0.019
Discount rate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Acquisition-related contingent liability		0.104
Discount rate | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Acquisition-related contingent liability		0.080