Pension Plan and Postretirement Benefits Other Than Pension (Details 5) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Benefits
Pension Plan and Postretirement Benefits Other than Pension
Aggregate liability to participants	$ 50,300,000	$ 45,000,000
Other Postretirement Benefits
Pension Plan and Postretirement Benefits Other than Pension
Initial health care cost trend rate (as a percent)	9.01%	9.51%	10.00%
Number of years at which the rate reaches the ultimate trend rate	15 years
Rate to which the cost trend rate is assumed to decline (as a percent)	4.50%
Effect of 1% annual increase in assumed health care cost trend rates on the accumulated postretirement benefit obligation	1,200,000
Effect of 1% annual increase in assumed health care cost trend rates on the service and interest cost components	180,000
Effect of 1% annual decrease in assumed health care cost trend rates on the accumulated postretirement benefit obligation	985,000
Effect of 1% annual decrease in assumed health care cost trend rates on the service and interest cost components	150,000
Aggregate liability to participants	8,500,000	7,800,000
Current portion of postretirement liability	304,000	289,000	303,000
SERP
Pension Plan and Postretirement Benefits Other than Pension
Percentage of executive's base salary that is used to credit participants SERP accounts	4.00%
Aggregate liability to participants	$ 3,700,000	$ 3,700,000