Annual report pursuant to Section 13 and 15(d)

Income Taxes - Reconciliation of the Federal Statutory Income Tax Rate to the Effective Income Tax Rate (Details)

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Income Taxes - Reconciliation of the Federal Statutory Income Tax Rate to the Effective Income Tax Rate (Details)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]      
U.S. Statutory rate 21.00% 21.00% 34.00%
State income taxes, net of federal benefit 3.70% (3.73%) 0.37%
Stock-based compensation (0.81%) (45.01%) (30.40%)
Change in valuation allowance     (2.59%)
R&D credit, net of reserve (8.97%) (1.39%) (1.43%)
Expiration of net operating losses     2.76%
Effect of U.S tax law change     25.55%
Other (1.24%) 0.98% 0.92%
Effective income tax rate 13.68% (28.15%) 29.18%