Annual and transition report of foreign private issuers pursuant to Section 13 or 15(d)

Equity (Stock-based Compensation Plans) (Narrative) (Details)

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Equity (Stock-based Compensation Plans) (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Jan. 01, 2016
Vesting period 4 years      
Weighted average remaining contractual life 3 years 4 months 24 days      
Total intrinsic value of options exercised $ 4.6 $ 55.6 $ 160.1  
Unvested number of shares 1,385,030      
Unrecognized compensation cost $ 26.6      
Weighted average period over which unrecognized compensation cost will be recognized 3 years      
2012 Plan [Member]        
Expected option term 10 years      
Equity Incentive Plan, shares authorized 2,700,000      
2012 Plan [Member] | Subsequent event [Member]        
Increase of shares reserved       500,000
Restricted Stock [Member]        
Value of equity classified RSUs vested $ 2.8      
Unrecognized compensation cost $ 29.0      
Weighted average period over which unrecognized compensation cost will be recognized 2 years 8 months 12 days      
Employee Stock Option [Member]        
Expected option term 6 years      
Employee Stock Option [Member] | 2012 Plan [Member]        
Vesting period 4 years      
Minimum [Member] | Employee Stock Option [Member]        
Expected option term   4 years 2 months 12 days 5 years 1 month 6 days  
Maximum [Member] | Employee Stock Option [Member]        
Expected option term   6 years 6 months 5 years 2 months 12 days