UK Pension Plan (Tables)
 9 Months Ended
Sep. 30, 2012
U.K. Pension Plan [Abstract]  
U.K. Pension Plan
The components of net periodic benefit cost for the three and nine months ended September 30, 2012 and 2011 are as follows (in millions):
 
   
Three Months Ended
  
Nine Months Ended
 
   
September 30,
  
September 30,
 
   
2012
  
2011
  
2012
  
2011
 
Interest cost on projected benefit obligation
 $0.7  $1.0  $2.1  $2.9 
Expected return on plan assets
  (0.7)  (0.9)  (2.1)  (2.7)
Net amortization
  0.2   0.5   0.7   1.5 
Net pension expense
 $0.2  $0.6  $0.7  $1.7