Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation (Details)

v3.10.0.1
Stock-Based Compensation (Details) - USD ($)
$ / shares in Units, $ in Millions
 6 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Fair value assumptions    
Dividend rate 0.00%  
Options    
Unrecognized compensation cost options $ 7.0  
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition 1 year 7 months 6 days  
Common Stock, Capital Shares Reserved for Future Issuance 2,800,000  
2014 Plan | Awards | Series A common stock    
Options    
Outstanding beginning balance (in shares) 404,000  
Exercised (in shares) (7,000)  
Outstanding ending balance (in shares) 397,000  
Number of awards exercisable (in shares) 396,000  
WAEP Outstanding beginning balance (in dollars per share) $ 33.16  
WAEP options exercised (in dollars per share) 29.57  
WAEP Outstanding ending balance (in dollars per share) 33.23  
WAEP options exercisable (in dollars per share) $ 33.18  
Weighted average remaining contractual life outstanding 1 year 6 months  
Weighted average remaining contractual life exercisable 1 year 6 months  
Aggregate intrinsic value outstanding $ 17.0  
Aggregate intrinsic value exercisable $ 17.0  
2014 Plan | Awards | Series C common stock    
Options    
Outstanding beginning balance (in shares) 2,388,000  
Exercised (in shares) (35,000)  
Outstanding ending balance (in shares) 2,353,000  
Number of awards exercisable (in shares) 833,000  
WAEP Outstanding beginning balance (in dollars per share) $ 43.35  
WAEP options exercised (in dollars per share) 30.08  
WAEP Outstanding ending balance (in dollars per share) 43.55  
WAEP options exercisable (in dollars per share) $ 34.55  
Weighted average remaining contractual life outstanding 4 years 9 months 18 days  
Weighted average remaining contractual life exercisable 1 year 8 months 12 days  
Aggregate intrinsic value outstanding $ 76.0  
Aggregate intrinsic value exercisable $ 34.0  
2014 Plan | Options    
Options    
Options granted (in shares) 0  
Other liabilities | Skyhook | LTIPs | PARs and PSUs | Significant other observable inputs (Level 2)    
Options    
Deferred compensation $ 0.9 $ 1.2