Stock-based Compensation Plans (Summary of Restricted Stock Activity) (Parenthetical) (Details)	12 Months Ended
	Dec. 31, 2018 shares
Time-based Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted Stock Award, Forfeitures	19,655
Performance-based restricted stock units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted Stock Award, Forfeitures	43,449
Market-based restricted stock units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted Stock Award, Forfeitures	2,705