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Stockholder's Equity (Schedule of Restricted Stock Unit Activity Under Stock Plans) (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Number of Restricted Stock Units    
Unvested ending balance (in shares) 1,869  
Restricted stock units    
Number of Restricted Stock Units    
Unvested beginning balance (in shares) [1] 1,745  
Granted (in shares) [1] 846  
Vested (in shares) [1] (524)  
Cancelled (in shares) [1] (198)  
Unvested ending balance (in shares) [1] 1,869 1,745
Weighted-Average Grant Date Fair Value    
Unvested beginning balance, weighted-average grant date fair value (in usd per share) $ 14.24  
Granted (in usd per share) 21.14  
Vested (in usd per share) 14.26  
Cancelled (in usd per share) 16.08  
Unvested ending balance, weighted-average grant date fair value (in usd per share) $ 16.95 $ 14.24
Weighted-Average Remaining Service Period 4 years 9 months 18 days 2 years 3 months 14 days
Aggregate Intrinsic Value [2] $ 71,816 $ 30,313
[1] Includes certain restricted stock units with service, performance-based or market-based vesting criteria.
[2] The aggregate intrinsic value is calculated as the difference of our closing stock price as of December 31, 2018 and December 31, 2017 multiplied by the number of restricted stock units outstanding as of December 31, 2018 and December 31, 2017, respectively.