Financial Instruments and Fair Value Measurements - Measurements on Recurring Basis (Details) - Recurring basis - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financial instruments and fair value measurements
Cash equivalents	$ 5,348	$ 89,964
Total	115,662	141,809
Level 1
Financial instruments and fair value measurements
Cash equivalents	5,348	89,964
Total	115,323	139,126
Level 2
Financial instruments and fair value measurements
Total	339	2,683
Unrestricted available-for-sale, Debt securities
Financial instruments and fair value measurements
Investments	109,975	48,051
Unrestricted available-for-sale, Debt securities \| Level 1
Financial instruments and fair value measurements
Investments	109,975	47,991
Unrestricted available-for-sale, Debt securities \| Level 2
Financial instruments and fair value measurements
Investments		60
Equity securities
Financial instruments and fair value measurements
Investments	339	2,623
Equity securities \| Level 2
Financial instruments and fair value measurements
Investments	339	2,623
Restricted
Financial instruments and fair value measurements
Investments		1,171
Restricted \| Level 1
Financial instruments and fair value measurements
Investments		1,171
Money Market Funds
Financial instruments and fair value measurements
Cash equivalents	5,348	10,973
Money Market Funds \| Level 1
Financial instruments and fair value measurements
Cash equivalents	5,348	10,973
U.S. Treasury Bills
Financial instruments and fair value measurements
Cash equivalents		78,991
U.S. Treasury Bills \| Level 1
Financial instruments and fair value measurements
Cash equivalents		78,991
U.S. Treasury Bills \| Unrestricted available-for-sale, Debt securities
Financial instruments and fair value measurements
Investments	109,975	47,991
U.S. Treasury Bills \| Unrestricted available-for-sale, Debt securities \| Level 1
Financial instruments and fair value measurements
Investments	109,975	47,991
Corporate debt securities \| Unrestricted available-for-sale, Debt securities
Financial instruments and fair value measurements
Investments		60
Corporate debt securities \| Unrestricted available-for-sale, Debt securities \| Level 2
Financial instruments and fair value measurements
Investments		60
Preferred stock \| Equity securities
Financial instruments and fair value measurements
Investments	339	2,623
Preferred stock \| Equity securities \| Level 2
Financial instruments and fair value measurements
Investments	$ 339	2,623
Short-term bond \| Restricted
Financial instruments and fair value measurements
Investments		1,171
Short-term bond \| Restricted \| Level 1
Financial instruments and fair value measurements
Investments		$ 1,171

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

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+ References

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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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