Retirement Benefits (Schedule of Net Benefit Costs) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Retirement Benefits [Abstract]
Interest cost	$ 2,716	$ 2,675	$ 2,631
Amortization of unrecognized:
Prior service costs	3,023	3,023	3,023
Net actuarial loss	1,330	424	0
Net periodic pension cost	$ 7,069	$ 6,122	$ 5,654