Investments and Fair Value Measures and Disclosures - Investments (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Summary of Investment Holdings [Line Items]
Average remaining maturities for short-term available for sale investments			3 months
Average remaining maturities for long-term available for sale investments			2 years
Proceeds from sales of available-for-sale investments	$ 0	$ 0	$ 0	$ 0
Other Assets [Member]
Summary of Investment Holdings [Line Items]
Direct investments in privately-held companies	24,400,000		24,400,000		$ 22,500,000
Private Equity Funds [Member]
Summary of Investment Holdings [Line Items]
Alternative Investment	$ 19,200,000		$ 19,200,000		$ 11,300,000