Retirement Plans - Assumptions used to determine the net periodic benefit cost and benefit obligations (Details) (Pension Plans [Member])	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for net periodic pension cost	4.50%	5.25%	5.75%
Discount rate for benefit obligations	3.75%	4.50%	5.25%
Expected long-term return of plan assets	8.00%	8.00%	8.00%