Share-Based Compensation Arrangements (Nonvested Performance Share Unit Awards Outstanding) (Details) - Performance Based Nonvested Shares [Member]	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance share awards, shares vesting	93,604
2018 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance share awards granted, grant date fair value | $ / shares	$ 54.25
Performance share awards, shares vesting percentages	140.00%
Performance share awards, shares vesting	41,454
2017 Grant [Domain]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance share awards granted, grant date fair value | $ / shares	$ 51.85
Performance share awards, shares vesting percentages	150.00%
Performance share awards, shares vesting	24,150
2016 Grant [Domain]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance share awards granted, grant date fair value | $ / shares	$ 36.11
Performance share awards, shares vesting percentages	140.00%
Performance share awards, shares vesting	28,000