Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation Stock-Based Compensation - Summary of Non-Employee RSU Activity (Details)

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Stock-Based Compensation Stock-Based Compensation - Summary of Non-Employee RSU Activity (Details) - Restricted Stock Units (RSUs) - shares
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vested as of December 31 (in shares) 116,900  
Outstanding as of December 31 (in shares) 670,800 324,600
2016 Directors' Plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vested as of December 31 (in shares) 203,261 174,442
Granted (in shares) 57,012 67,288
Outstanding as of December 31 (in shares) 260,273 241,730