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Fair Value Measurement - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Assets:
Money market funds	$ 262,941	$ 268,918	$ 261,585
Marketable securities:	26,793	29,878
Liabilities:
Deferred payments	85,210	95,518
Recurring
Assets:
Total assets at fair value on a recurring basis	33,357	34,012
Money market funds \| Recurring
Assets:
Money market funds	6,564	4,134
Tax-exempt municipal securities
Assets:
Marketable securities:	18,237	18,817
Tax-exempt municipal securities \| Recurring
Assets:
Marketable securities:	18,237	18,817
Corporate debt securities
Assets:
Marketable securities:	8,556	11,061
Corporate debt securities \| Recurring
Assets:
Marketable securities:	8,556	11,061
Deferred payments \| Recurring
Liabilities:
Deferred payments		658
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) \| Recurring
Assets:
Total assets at fair value on a recurring basis	6,564	4,134
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) \| Money market funds \| Recurring
Assets:
Money market funds	6,564	4,134
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) \| Tax-exempt municipal securities \| Recurring
Assets:
Marketable securities:	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) \| Corporate debt securities \| Recurring
Assets:
Marketable securities:	0	0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) \| Deferred payments \| Recurring
Liabilities:
Deferred payments		0
Significant Other Observable Inputs (Level 2) \| Recurring
Assets:
Total assets at fair value on a recurring basis	26,793	29,878
Significant Other Observable Inputs (Level 2) \| Money market funds \| Recurring
Assets:
Money market funds	0	0
Significant Other Observable Inputs (Level 2) \| Tax-exempt municipal securities \| Recurring
Assets:
Marketable securities:	18,237	18,817
Significant Other Observable Inputs (Level 2) \| Corporate debt securities \| Recurring
Assets:
Marketable securities:	8,556	11,061
Significant Other Observable Inputs (Level 2) \| Deferred payments \| Recurring
Liabilities:
Deferred payments		0
Significant Unobservable Inputs (Level 3) \| Recurring
Assets:
Total assets at fair value on a recurring basis	0	0
Significant Unobservable Inputs (Level 3) \| Money market funds \| Recurring
Assets:
Money market funds	0	0
Significant Unobservable Inputs (Level 3) \| Tax-exempt municipal securities \| Recurring
Assets:
Marketable securities:	0	0
Significant Unobservable Inputs (Level 3) \| Corporate debt securities \| Recurring
Assets:
Marketable securities:	$ 0	0
Significant Unobservable Inputs (Level 3) \| Deferred payments \| Recurring
Liabilities:
Deferred payments		$ 658