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Stock-Based Compensation Expense - ESPP Fair Value Assumptions (Details) - 2014 ESPP - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Apr. 22, 2014
Dec. 31, 2016
Dec. 31, 2015
Stock-Based Compensation      
Length of purchase intervals under ESPP plan 6 months    
Percentage of purchase price per share 85.00%    
Maximum payroll deductions allowed to purchase shares of common stock on purchase dates (as a 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 (per share)   $ 25  
Shares of common stock reserved for future issuance   1,280,569  
Assumptions used to compute the fair value of stock option awards      
Expected life (in years)   6 months 6 months
Dividend yield (as a percent)   0.00% 0.00%
Unrecognized compensation cost related to awards   $ 29  
Minimum      
Assumptions used to compute the fair value of stock option awards      
Volatility (as a percent)   32.00% 28.00%
Risk-free interest rate (as a percent)   0.46% 0.07%
Maximum      
Stock-Based Compensation      
Shares of common stock reserved for future issuance   2,000,000  
Assumptions used to compute the fair value of stock option awards      
Volatility (as a percent)   35.00% 35.00%
Risk-free interest rate (as a percent)   0.49% 0.22%
Weighted-average period over which unrecognized compensation cost is expected to be recognized   1 year