Investments and Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Dec. 31, 2019
Marketable securities
Amortized Cost	$ 96,343	$ 191,314
Gross Unrealized Gains	531	95
Gross Unrealized Losses		(20)
Fair Value	96,874	191,389
Assets:
Investments	96,874	191,389
Transfers between Level 1, Level 2 or Level 3
Transfer from Level 1 to Level 2, assets	0
Transfer from Level 2 to Level 1, assets	0
Transfers into Level 3, assets	0
Transfer out of Level 3, assets	0
Transfer from Level 1 to Level 2, liabilities	0
Transfer from Level 2 to Level 1, liabilities	0
Transfers into Level 3, liabilities	0
Transfer out of Level 3, liabilities	0
U.S. treasury bills and notes
Marketable securities
Amortized Cost	94,843
Gross Unrealized Gains	529
Gross Unrealized Losses
Fair Value	95,372
Assets:
Investments	95,372
U.S. government agency bonds
Marketable securities
Amortized Cost	1,500	1,498
Gross Unrealized Gains	2	4
Gross Unrealized Losses
Fair Value	1,502	1,502
Assets:
Investments	1,502	1,502
U.S. treasury notes
Marketable securities
Amortized Cost		189,816
Gross Unrealized Gains		91
Gross Unrealized Losses		(20)
Fair Value		189,887
Assets:
Investments		189,887
Recurring
Assets:
Assets	241,391	283,287
Recurring \| Money market funds
Assets:
Cash equivalents	133,017	91,898
Recurring \| U.S. treasury bills and notes
Marketable securities
Fair Value	95,372
Assets:
Investments	95,372
Recurring \| U.S. treasury bills
Assets:
Cash equivalents	11,500
Recurring \| U.S. government agency bonds
Marketable securities
Fair Value	1,502	1,502
Assets:
Investments	1,502	1,502
Recurring \| U.S. treasury notes
Marketable securities
Fair Value		189,887
Assets:
Investments		189,887
Recurring \| Level 1
Assets:
Assets	133,017	91,898
Recurring \| Level 1 \| Money market funds
Assets:
Cash equivalents	133,017	91,898
Recurring \| Level 2
Assets:
Assets	108,374	191,389
Recurring \| Level 2 \| U.S. treasury bills and notes
Marketable securities
Fair Value	95,372
Assets:
Investments	95,372
Recurring \| Level 2 \| U.S. treasury bills
Assets:
Cash equivalents	11,500
Recurring \| Level 2 \| U.S. government agency bonds
Marketable securities
Fair Value	1,502	1,502
Assets:
Investments	$ 1,502	1,502
Recurring \| Level 2 \| U.S. treasury notes
Marketable securities
Fair Value		189,887
Assets:
Investments		$ 189,887

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