Quarterly report pursuant to Section 13 or 15(d)

Employee Stock Plans - Summary of Restricted Stock Awards and Units (Details)

v3.10.0.1
Employee Stock Plans - Summary of Restricted Stock Awards and Units (Details) - $ / shares
 9 Months Ended 12 Months Ended
Sep. 30, 2018
Dec. 31, 2017
2010 Plan    
Stock-based compensation    
Maximum number of shares of common stock that may be issued 2,130,000  
Performance Share Unit Awards | 2010 Plan    
Weighted Average Grant Date Fair Value    
Granted (in dollars per share) $ 37.40  
Restricted Stock Unit Awards    
Shares    
Unvested at the beginning of the period (in shares) 47,542  
Granted (in shares) 134,804  
Vested (in shares) (96,034)  
Unvested at the end of the period (in shares) 86,312 47,542
Expected to vest in the future, at the end of the period (in shares) 86,312  
Weighted Average Grant Date Fair Value    
Unvested at the beginning of the period (in dollars per share) $ 23.95  
Granted (in dollars per share) 35.73  
Vested (in dollars per share) 30.54  
Cancelled and forfeited (in dollars per share) 0.00  
Unvested at the end of the period (in dollars per share) 35.01 $ 23.95
Expected to vest in the future, at the end of the period (in dollars per share) $ 35.01  
Weighted Average Remaining Contractual Term    
Unvested at the beginning of the period 9 months 29 days 10 months 2 days
Granted 6 months  
Unvested at the end of the period 9 months 29 days 10 months 2 days
Expected to vest in future, at the end of the period 9 months 29 days