Retirement Benefits - Assumptions (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Benefit Obligation Assumptions
Discount rate	4.15%
Assumed Health Care Cost Trend Rates
Medical inflation rate assumed for next fiscal year	7.50%
Ultimate health care cost trend rate	4.80%
Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates
1% Increase, Effect on post-retirement benefit obligation	92		97
1% Decrease, Effect on post-retirement benefit obligation	92		85
1% Increase, Effect on service and interest cost components	4		5
1% Decrease, Effect on service and interest cost components	4		4
Qualified Pension Benefits
Benefit Obligation Assumptions
Discount rate	4.15%	[1]	4.75%	[1]	5.15%	[1]
Rate of compensation increase	4.50%		4.50%		4.50%
Medical trend rate	0.00%		0.00%		0.00%
Benefit Cost Assumptions
Discount rate	4.75%		5.15%		5.75%
Rate of plan assets	7.75%				8.00%
Rate of compensation increase	4.50%		4.50%		4.50%
Medical trend rate	0.00%		0.00%		0.00%
SERP Pension Benefits
Benefit Obligation Assumptions
Discount rate	4.15%	[1]	4.75%	[1]	5.15%	[1]
Rate of compensation increase	4.50%		4.50%		4.50%
Medical trend rate	0.00%		0.00%		0.00%
Benefit Cost Assumptions
Discount rate	4.75%		5.15%		5.75%
Rate of plan assets	0.00%		0.00%		0.00%
Rate of compensation increase	4.50%		4.50%		4.50%
Medical trend rate	0.00%		0.00%		0.00%
Other Benefits
Benefit Obligation Assumptions
Discount rate	4.15%	[1]	4.75%	[1]	5.15%	[1]
Rate of compensation increase	4.50%		4.50%		4.50%
Medical trend rate	7.50%		7.50%		8.00%
Benefit Cost Assumptions
Discount rate	4.75%		5.15%		5.75%
Rate of plan assets	7.50%		7.80%		7.80%
Rate of compensation increase	4.50%		4.50%		4.50%
Medical trend rate	7.50%		8.00%		8.50%

[1] The Company calculates the present value of the pension liability using a discount rate of 4.15% which represents the single-rate equivalent of the AA rated corporate bond yield curve.