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, 2012	Dec. 31, 2011	Dec. 31, 2010
Share Options [Member]
Number of Share Options:
Beginning of period	712,061
Granted	106,775	57,450	83,700
Exercised	(150,039)
Forfeited or expired	(23,000)
End of period	645,797	712,061
Options exercisable	390,347
Options expected to vest in future periods	255,450
Weighted Average Exercise Price (in dollars per share):
Beginning of period	$ 22.96
Granted	$ 23.37
Exercised	$ 20.06
Forfeited or expired	$ 26.33
End of period	$ 23.58	$ 22.96
Options exercisable	$ 25.35
Options expected to vest in future periods	$ 20.89
Outstanding Weighted Average Remaining Contractual Term	5 years
Exercisable Weighted Average Remaining Contractual Term	2 years 8 months 12 days
Expected to Vest Weighted Average Remaining Contractual Term	8 years 4 months 24 days
Outstanding Aggregate Intrinsic Value	$ 2,043
Exercisable Aggregate Intrinsic Value	658
Expected to Vest Aggregate Intrinsic Value	$ 1,385