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Fair Value Measurements Fair Value Measurements (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Assets, Fair Value Disclosure [Abstract] |  |
Money Market Funds | $ 551,213 | $ 363,075
US Government Securities, at Carrying Value | 10,531 | 34,728
Municipal bonds | 23,998 | 0
Total | 585,742 | 397,803
US Treasury Securities [Member] |  |
Debt Securities, Available-for-sale [Abstract] |  |
Available-for-sale Securities, Amortized Cost Basis | 10,530 | 34,716
Available-for-sale Securities, Gross Unrealized Gain | 1 | 13
Available-for-sale Securities, Gross Unrealized Loss | 0 | (1)
Fair Value | 10,531 | 34,728
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract] |  |
Fair Value | 10,531 | 34,728
Municipal Bond [Member] |  |
Debt Securities, Available-for-sale [Abstract] |  |
Available-for-sale Securities, Amortized Cost Basis | 23,994 |
Available-for-sale Securities, Gross Unrealized Gain | 8 |
Available-for-sale Securities, Gross Unrealized Loss | (4) |
Fair Value | 23,998 |
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract] |  |
Fair Value | 23,998 |
Level 1 [Member] |  |
Assets, Fair Value Disclosure [Abstract] |  |
Money Market Funds | 551,213 | 363,075
US Government Securities, at Carrying Value | 10,531 | 34,728
Municipal bonds | 0 | 0
Total | 561,744 | 397,803
Level 2 [Member] |  |
Assets, Fair Value Disclosure [Abstract] |  |
Money Market Funds | 0 | 0
US Government Securities, at Carrying Value | 0 | 0
Municipal bonds | 23,998 | 0
Total | $ 23,998 | $ 0

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References 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 + Details
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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References No definition available. + Details
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- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References No definition available. + Details
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- Definition Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 + Details
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- Definition Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 + Details
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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 No definition available. + Details
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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 + Details
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