XML 103 R77.htm IDEA: XBRL DOCUMENT v3.8.0.1
Stock-Based Compensation - Employee Stock Purchase Plan (Details) - 2014 ESPP - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Apr. 22, 2014
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Assumptions used to compute the fair value of stock option awards        
Expected life (in years)   6 months 6 months 6 months
Dividend yield (percent)   0.00% 0.00% 0.00%
Length of purchase intervals under ESPP plan 6 months      
Percentage of purchase price per share (percent) 85.00%      
Maximum payroll deductions allowed to purchase shares of common stock on purchase dates (percent) 15.00%      
Maximum number of common stock permitted to be purchased by employees on any one purchase date under ESPP 5,000      
Maximum fair value of shares permitted to be purchased under ESPP (usd per share) $ 25      
Shares of common stock reserved for future issuance (shares)   1,001,658    
Unrecognized compensation cost related to awards   $ 34    
Minimum        
Assumptions used to compute the fair value of stock option awards        
Volatility (percent)   42.00% 32.00% 28.00%
Risk-free interest rate (percent)   0.70% 0.46% 0.07%
Maximum        
Assumptions used to compute the fair value of stock option awards        
Volatility (percent)   52.00% 35.00% 35.00%
Risk-free interest rate (percent)   1.10% 0.49% 0.22%
Shares of common stock reserved for future issuance (shares)   2,000,000    
Weighted-average period over which unrecognized compensation cost is expected to be recognized   1 year