Share-Based Compensation Arrangements (Share Options Activity) (Details) (Share Options [Member], USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share Options [Member]
Number of Share Options:
Beginning of period	428,388
Granted	25,850	54,600	106,775
Exercised	(89,511)
Forfeited or expired	(7,250)
End of period	357,477	428,388
Options exercisable	192,627
Options expected to vest in future periods	164,850
Weighted Average Exercise Price (in dollars per share):
Beginning of period	$ 24.50
Granted	$ 32.74
Exercised	$ 24.66
Forfeited or expired	$ 27.20
End of period	$ 24.99	$ 24.50
Options exercisable	$ 22.60
Options expected to vest in future periods	$ 27.79
Outstanding Weighted Average Remaining Contractual Term	5 years 9 months 17 days
Exercisable Weighted Average Remaining Contractual Term	3 years 8 months 12 days
Expected to Vest Weighted Average Remaining Contractual Term	8 years 3 months
Outstanding Aggregate Intrinsic Value	$ 5,428
Exercisable Aggregate Intrinsic Value	3,386
Expected to Vest Aggregate Intrinsic Value	$ 2,042