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Common Stock and Stockholders' Equity - Employee Stock Purchase Plan (Details) - USD ($)
$ in Thousands
1 Months Ended 12 Months Ended
Jul. 31, 2015
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Employee Stock Purchase Plan        
Stock-based compensation   $ 66,702 $ 43,769 $ 30,597
ESPP        
Employee Stock Purchase Plan        
Shares reserved for issuance under the plan (in shares)     645,258  
Maximum offering period 27 months 27 months    
Stock purchase price as a percentage of fair value (as a percent) 85.00% 85.00%    
Issuance of stock under employee stock purchase plan (in shares)   64,497 85,218  
Remaining shares available for issuance under the plan (in shares)   461,650    
Stock-based compensation   $ 1,200 $ 1,000 $ 600
Unrecognized compensation cost   $ 600    
Period over which unrecognized compensation cost is expected to be recognized   4 months 24 days