Stock-Based Incentive Compensation Plans (Summary of activity for performance shares) (Details) - Performance Shares [Member]	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Shares:
Outstanding as of beginning of year (in shares) | shares	471,071
Granted (in shares) | shares	233,039
Vested (in shares) | shares	(134,282)
Forfeited (in shares) | shares	(27,120)
Outstanding as of end of year (in shares) | shares	542,708
Weighted-Average Grant Date Fair Value
Weighted-average grant date fair value, outstanding as of beginning of year (in dollars per share) | $ / shares	$ 77.29
Weighted-average grant date fair value, granted (in dollars per share) | $ / shares	64.62
Weighted-average grant date fair value, vested (in dollars per share) | $ / shares	79.61
Weighted-average grant date fair value, forfeited (in dollars per share) | $ / shares	70.54
Weighted-average grant date fair value, outstanding as of end of year (in dollars per share) | $ / shares	$ 71.61