Marketable Securities (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Investment in marketable securities		$ 0
Short-term marketable securities
Gross Amortized Cost	$ 184,634,000
Total Unrealized Gains	282,000
Total Unrealized Losses	0
Fair Value	184,916,000
Long-term marketable securities
Gross Amortized Cost	101,726,000
Total Unrealized Gains	0
Total Unrealized Losses	(142,000)
Fair Value	101,584,000
Commercial paper
Short-term marketable securities
Gross Amortized Cost	89,324,000
Total Unrealized Gains	127,000
Total Unrealized Losses	0
Fair Value	89,451,000
Corporate bonds
Short-term marketable securities
Gross Amortized Cost	75,325,000
Total Unrealized Gains	153,000
Total Unrealized Losses	0
Fair Value	75,478,000
Long-term marketable securities
Gross Amortized Cost	66,725,000
Total Unrealized Gains	0
Total Unrealized Losses	(135,000)
Fair Value	66,590,000
U.S. Treasury bills
Short-term marketable securities
Gross Amortized Cost	19,985,000
Total Unrealized Gains	2,000
Total Unrealized Losses	0
Fair Value	19,987,000
Long-term marketable securities
Gross Amortized Cost	35,001,000
Total Unrealized Gains	0
Total Unrealized Losses	(7,000)
Fair Value	$ 34,994,000