Share-Based Payment Arrangements (Summary of Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate Intrinsic Value, Outstanding at Beginning	$ 3,734
Aggregate Intrinsic Value, Outstanding at Ending		$ 3,734
Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Outstanding at Beginning	456,258
Number of Shares, Exercised	(350,744)
Number of Shares, Cancelled/Forfeited	(538)
Number of Shares, Expired	(16,675)
Number of Shares, Outstanding at Ending	88,301	456,258
Number of Shares, Exercisable at Ending	88,301
Weighted Average Exercise Price, Outstanding at Beginning	$ 35.91
Weighted Average Exercise Price, Exercised	34.65
Weighted Average Exercise Price, Cancelled/Forfeited	32.09
Weighted Average Exercise Price, Expired	68.18
Weighted Average Exercise Price, Outstanding at Ending	34.84	$ 35.91
Weighted Average Exercise Price, Exercisable at Ending	$ 34.84
Weighted Average Remaining Contractual Term (Years)	2 years 9 months 18 days	3 years 6 months
Weighted Average Remaining Contractual Term (Years), Exercisable at Ending	2 years 9 months 18 days
Aggregate Intrinsic Value, Exercised	$ 4,304
Aggregate Intrinsic Value, Cancelled/Forfeited	6
Aggregate Intrinsic Value, Outstanding at Ending	1,294
Aggregate Intrinsic Value, Exercisable at Ending	$ 1,294