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Cash Equivalents and Marketable Securities - Classification of Cash Equivalents and Marketable Securities (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Classified as:    
Cash equivalents $ 113,693 $ 31,707
Marketable securities - current 188,451 100,011
Marketable securities - noncurrent 2,000  
Total cash equivalents and marketable securities $ 304,144 131,718
Contractual maturities    
Maximum period of current contractual maturities 1 year  
Minimum period of noncurrent contractual maturities 1 year  
Maximum period of Noncurrent contractual maturities 2 years  
Realized Gain (loss) $ 0 $ 0