Fair Value (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	$ 66,649,000	$ 73,649,000
Cash collateral payable to trade counterparties	8,500,000	300,000
Fair value, assets, Level 2 to Level 3 transfers, amount	$ 0
Contingent payment arrangements		17,400,000
Contingent consideration payable, term	5 years
Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent payment arrangements	$ 23,704,000	22,911,000
Recurring | Contingent Payment Arrangements
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent payment arrangements	23,700,000	22,900,000
Software publishing company
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	1,000,000.0	1,000,000
Start-up company
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments		900,000
Equity method investee
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	2,700,000	2,900,000
Broker dealer exchange memberships
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other investments	$ 3,200,000	3,200,000
2016 Acquisition
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Change in estimate for contingent consideration		$ 3,100,000
2016 Acquisition | Revenue growth rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Acquisition-related contingent liability	0.50
2016 Acquisition | Discount rate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Acquisition-related contingent liability	0.030
Autonomous | Revenue growth rate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Acquisition-related contingent liability	0.007
Autonomous | Revenue growth rate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Acquisition-related contingent liability	0.025
Autonomous | Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Acquisition-related contingent liability	0.104
Autonomous | Risk-free rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Acquisition-related contingent liability	0.035
Autonomous | Market price of risk adjustment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Acquisition-related contingent liability	0.069