Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation and Employee Benefit Plans - ESPP (Details)

v3.8.0.1
Stock-Based Compensation and Employee Benefit Plans - ESPP (Details) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock Issued During Period, Shares, Employee Stock Purchase Plans (216,302)    
ESPP [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Per Share Weighted Average Price of Shares Purchased $ 19.71    
Employee Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield 0.00% 0.00% 0.00%
Expected life (in years)   6 months 6 months
Minimum [Member] | Employee Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted-average grant date fair value per share $ 6.20 $ 5.85 $ 2.25
Risk-free interest rate 60.00% 0.38% 0.09%
Expected life (in years) 4 months 17 days    
Volatility 29.56% 49.94% 32.65%
Maximum [Member] | Employee Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted-average grant date fair value per share $ 7.46 $ 6.20 $ 5.02
Risk-free interest rate 1.39% 0.60% 0.33%
Expected life (in years) 6 months    
Volatility 49.94% 53.94% 59.14%