Retirement Benefits (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,460	$ 2,729
Interest cost	2,542	2,074
Expected return on plan assets	(2,823)	(2,122)
Amortization of prior service cost	13	13
Amortization of net (income) loss	1,091	1,904
Net periodic benefit cost	3,283	4,598
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	407	499
Interest cost	342	277
Amortization of net (income) loss	82	154
Net periodic benefit cost	$ 831	$ 930