XML 125 R100.htm IDEA: XBRL DOCUMENT v3.8.0.1
Share-Based Compensation Plans - Restricted Stock Unit Awards (Details) - Restricted Stock Units, Liability - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of shares granted (in shares) 292,400 148,860
Outstanding units (in shares) 386,360  
Award vesting period 3 years  
Deferred compensation liability $ 8.8 $ 2.7