Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity (Stock Option Plan Activity) (Details)

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Stockholders' Equity (Stock Option Plan Activity) (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
3 Months Ended 12 Months Ended
Mar. 31, 2014
Dec. 31, 2013
Shares    
Balance, Beginning 1,746,709  
Granted 332,000  
Exercised (203,933)  
Forfeited (43,488)  
Cancelled (1,441)  
Balance, Ending 1,829,847 1,746,709
Exercisable 854,353  
Options vested and expected to vest 1,829,847  
Weighted Average Exercise Price    
Balance, Beginning $ 16.79  
Granted (in usd per share) $ 74.42  
Exercised (in usd per share) $ 15.73  
Forfeited (in usd per share) $ 16.72  
Cancelled (in usd per share) $ 78.78  
Balance, Ending $ 27.32 $ 16.79
Exercisable $ 15.55  
Options vested and expected to vest $ 27.32  
Weighted Average Remaining Contractual Term in Years    
Weighted average remaining contractual term in years 7 years 10 months 10 days 7 years 6 months 26 days
Exercisable 6 years 9 months 4 days  
Options vested and expected to vest 7 years 10 months 10 days  
Aggregate Intrinsic Value    
Aggregate intrinsic value $ 75,528 $ 62,705
Exercisable 44,234  
Options vested and expected to vest $ 75,528