Retirement Plan Benefits - Actual Allocation of the Assets in the Pension Plan (Details)	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Actual allocation of the Pension Plan assets	100.00%	100.00%
U.S. large capitalization equities
Defined Benefit Plan Disclosure [Line Items]
Actual allocation of the Pension Plan assets	28.00%	29.00%
U.S. small capitalization equities
Defined Benefit Plan Disclosure [Line Items]
Actual allocation of the Pension Plan assets	6.00%	6.00%
International equities
Defined Benefit Plan Disclosure [Line Items]
Actual allocation of the Pension Plan assets	8.00%	7.00%
U.S. long-duration fixed income
Defined Benefit Plan Disclosure [Line Items]
Actual allocation of the Pension Plan assets	55.00%	55.00%
High yield fixed income
Defined Benefit Plan Disclosure [Line Items]
Actual allocation of the Pension Plan assets	3.00%	3.00%