Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Financial assets:
Equity warrant investment	$ 1,067	$ 1,323
Total financial assets	875,800	671,410
Financial liabilities:
Success payment liabilities	9,486	5,773
Total financial liabilities	9,486	5,773
U.S. Treasury securities
Financial assets:
Marketable securities	289,706	202,701
U.S. government agency securities
Financial assets:
Marketable securities	93,626	205,764
Corporate debt securities
Financial assets:
Marketable securities	285,156	211,109
Money market funds
Financial assets:
Cash and cash equivalents	206,245	50,513
Level 1
Financial assets:
Equity warrant investment	0	0
Total financial assets	206,245	50,513
Financial liabilities:
Success payment liabilities	0	0
Total financial liabilities	0	0
Level 1 | U.S. Treasury securities
Financial assets:
Marketable securities	0	0
Level 1 | U.S. government agency securities
Financial assets:
Marketable securities	0	0
Level 1 | Corporate debt securities
Financial assets:
Marketable securities	0	0
Level 1 | Money market funds
Financial assets:
Cash and cash equivalents	206,245	50,513
Level 2
Financial assets:
Equity warrant investment	0	0
Total financial assets	668,488	619,574
Financial liabilities:
Success payment liabilities	0	0
Total financial liabilities	0	0
Level 2 | U.S. Treasury securities
Financial assets:
Marketable securities	289,706	202,701
Level 2 | U.S. government agency securities
Financial assets:
Marketable securities	93,626	205,764
Level 2 | Corporate debt securities
Financial assets:
Marketable securities	285,156	211,109
Level 2 | Money market funds
Financial assets:
Cash and cash equivalents	0	0
Level 3
Financial assets:
Equity warrant investment	1,067	1,323
Total financial assets	1,067	1,323
Financial liabilities:
Success payment liabilities	9,486	5,773
Total financial liabilities	9,486	5,773
Level 3 | U.S. Treasury securities
Financial assets:
Marketable securities	0	0
Level 3 | U.S. government agency securities
Financial assets:
Marketable securities	0	0
Level 3 | Corporate debt securities
Financial assets:
Marketable securities	0	0
Level 3 | Money market funds
Financial assets:
Cash and cash equivalents	$ 0	$ 0