Retirement Benefits (Schedule of Net Benefit Costs) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Retirement Benefits [Abstract]
Interest cost	$ 2,476	$ 2,716	$ 2,675
Amortization of unrecognized:
Prior service costs	3,023	3,023	3,023
Net actuarial loss	2,197	1,330	424
Net periodic pension cost	$ 7,696	$ 7,069	$ 6,122