Investments (Narrative) (Details) - USD ($)	1 Months Ended	3 Months Ended
	Jan. 31, 2021	Mar. 31, 2021	Mar. 31, 2020	Feb. 28, 2021	Dec. 31, 2020
Investments [Abstract]
Equity method investments		$ 95,300,000		$ 25,500,000	$ 69,500,000
Investments in marketable equity securities		11,200,000			62,400,000
Sale of marketable securities	$ 51,000,000.0
Realized loss	$ 5,400,000
Unrealized gain (loss) on marketable securities		0	$ 1,100,000
Investments in non-marketable equity securities		$ 36,000,000.0			$ 35,800,000
Write-down of non-marketable equity securities and note receivable			$ 20,000,000.0