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Stockholders' Equity (Details Textual)
12 Months Ended
May 31, 2012
shares
May 29, 2009
shares
Dec. 31, 2015
USD ($)
right
$ / shares
shares
Dec. 31, 2014
USD ($)
$ / shares
shares
Dec. 31, 2013
USD ($)
$ / shares
shares
Sep. 30, 2015
USD ($)
Aug. 31, 2014
USD ($)
$ / shares
shares
Employee Stock Purchase Plan [Abstract]              
Stock-based compensation expense | $     $ 12,458,000 $ 11,270,000 $ 5,666,000    
Preferred Stock [Abstract]              
Preferred stock authorized (shares)     5,000,000        
Preferred stock issued (shares)     0 0      
Preferred stock outstanding (shares)     0 0      
Shareholder Rights Plan and Warrants [Abstract]              
Warrants to purchase number of shares             3,264,643
Exercise price per share of warrants | $ / shares             $ 125.08
Corporate Share Repurchase [Abstract]              
Stock Repurchase Program, Authorized Amount | $           $ 200,000,000.0 $ 200,000,000.0
Stock Repurchased During Period, Shares     6,120 1,253,425      
Treasury Stock Acquired, Average Cost Per Share | $ / shares     $ 79.92 $ 54.20      
Stock Repurchased During Period, Value | $     $ 489,000 $ 67,955,000      
2006 Stockholder Rights Plan              
Shareholder Rights Plan and Warrants [Abstract]              
Number of rights per outstanding share of common stock | right     1        
Warrants to purchase number of shares     0.001        
Exercise price per share of warrants | $ / shares     $ 100        
Percentage acquisition of company's common stock causing warrants or rights to become exercisable     20.00%        
Percentage acquisition of company's common stock from tender offer causing warrants or rights to become exercisable     20.00%        
Warrants to purchase shares, stockholder other than acquiring person, exercise price percentage     200.00%        
Business combination, acquiring person discount (percent)     50.00%        
Series A Preferred Stock              
Preferred Stock [Abstract]              
Preferred stock authorized (shares)     1,600,000        
Stock Options              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Weighted-average grant date fair value per share of stock options | $ / shares     $ 35.39 $ 46.20 $ 14.28    
Intrinsic value of options exercised | $     $ 20,700,000 $ 15,300,000 $ 5,900,000    
Unrecognized compensation cost | $     $ 13,100,000        
Weighted-average period in which cost is expected to be recognized     2 years 4 months 10 days        
Cash received from options exercised | $     $ 8,700,000 $ 4,400,000 $ 3,000,000    
Restricted Stock              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Weighted-average period in which cost is expected to be recognized     1 year 7 months 2 days        
Award vesting period     3 years        
Unrecognized compensation cost, restricted stock | $     $ 4,700,000        
2002 Stock Incentive Plan | Stock Options              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Increase the number of shares under the 2002 Stock Incentive Plan 1,800,000 1,300,000          
Shares available for future option grants     700,000        
Employee Stock Purchase Plan [Abstract]              
Award expiration period     10 years        
Amended ESPP              
Employee Stock Purchase Plan [Abstract]              
Shares allowed to purchase in employee stock purchase plan     1,250        
Offering period of shares in employee stock purchase plan     6 months        
Percentage lesser of fair market value taken as purchase price of share     85.00%        
Discount rate     15.00%        
Common stock issued under amended ESSP (shares)     3,374 3,774 5,016    
Stock-based compensation expense | $     $ 56,000 $ 54,000 $ 45,000    
Revenue volatility (percent)     49.00% 40.00% 36.00%    
Award expiration period     6 months        
Shares issued under employee stock purchase plan     215,821        
Shares available for future purchases     72,367