Marketable Securities - Loss position (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Unrealized loss position for a period longer than twelve months	$ 0
Allowance for credit losses	0
Impairment charges	$ 0	$ 0	$ 0