XML 68 R57.htm IDEA: XBRL DOCUMENT v3.10.0.1
Stock Plans - Weighted Average Risk Assumptions (Details) - Performance Stock Unit
3 Months Ended 9 Months Ended
Mar. 31, 2018
$ / shares
Sep. 30, 2018
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Fair value per unit (dollars per share)   $ 84.79
Monte Carlo Approach    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Fair value per unit (dollars per share) $ 83.58  
Risk-free interest rate 2.36%  
Expected dividend yield 1.82%  
Expected volatility 28.30%  
MSA stock beta 1.240