Annual report pursuant to Section 13 and 15(d)

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

v3.8.0.1
Stock-Based Compensation Stock-Based Compensation - Summary of Non-Employee RSU Activity (Details) - Restricted Stock Units (RSUs) - shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vested as of December 31 (in shares) 213,600  
Outstanding as of December 31 (in shares) 231,600 362,800
2016 Directors' Plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vested as of December 31 (in shares) 140,146 93,428
Granted (in shares) 48,722 76,511
Outstanding as of December 31 (in shares) 188,868 163,040