Retirement Plans (Plan's Allocated Target and Ranges and Actual Weighted Average Asset Allocation by Investment Categories) (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Actual percentage	100.00%	100.00%
Maximum Percentage Of Any Security Value Of Total Plans Portfolio Vaue That Is Allowed	8.00%
Maximum Percentage Of Any Corporation Outstanding Shares That Is Allowed For Retirement Income Plan	5.00%
International Securities [Member]
Target percentage	10.00%
Actual percentage	7.00%	7.00%
Range minimum	4.00%
Range maximum	18.00%
Large Capitalization Securities [Member]
Target percentage	15.00%
Actual percentage	15.00%	18.00%
Range minimum	8.00%
Range maximum	32.00%
Small And Mid Capitalization Securities [Member]
Target percentage	5.00%
Actual percentage	7.00%	8.00%
Range minimum	3.00%
Range maximum	15.00%
Global Asset Allocation [Member]
Target percentage	10.00%
Actual percentage	10.00%	0.00%
Range minimum	0.00%
Range maximum	15.00%
Partnership Interest [Member]
Target percentage	10.00%
Actual percentage	6.00%	9.00%
Range minimum	0.00%
Range maximum	15.00%
Extended Duration Fixed Income [Member]
Target percentage	50.00%
Actual percentage	24.00%	20.00%
Range minimum	20.00%
Range maximum	80.00%
Domestic Core Debt Securities [Member]
Actual percentage	14.00%	17.00%
Global bond high yield emerging markets [Member]
Actual percentage	13.00%	14.00%
Cash and short term investments [Member]
Target percentage	0.00%
Actual percentage	4.00%	7.00%
Range minimum	0.00%
Range maximum	5.00%