Retirement Plan Benefits - Weighted Average Target Asset Allocations (Details)	12 Months Ended
	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Weighted average target asset allocation	100.00%
U.S. large capitalization equities
Defined Benefit Plan Disclosure [Line Items]
Weighted average target asset allocation	17.00%
U.S. small capitalization equities
Defined Benefit Plan Disclosure [Line Items]
Weighted average target asset allocation	4.00%
International equities
Defined Benefit Plan Disclosure [Line Items]
Weighted average target asset allocation	4.00%
U.S. long-duration fixed income
Defined Benefit Plan Disclosure [Line Items]
Weighted average target asset allocation	75.00%
High yield fixed income
Defined Benefit Plan Disclosure [Line Items]
Weighted average target asset allocation	0.00%