Pension Plan and Postretirement Benefits Other Than Pension (Details 5) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Benefits
Pension Plan and Postretirement Benefits Other than Pension
Aggregate liability to participants	$ 32,500,000	$ 1,700,000
Other Postretirement Benefits
Pension Plan and Postretirement Benefits Other than Pension
Initial health care cost trend rate (as a percent)	8.04%	8.52%	9.01%
Number of years at which the rate reaches the ultimate trend rate	13 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	168,000
Effect of 1% annual decrease in assumed health care cost trend rates on the accumulated postretirement benefit obligation	1,000
Effect of 1% annual decrease in assumed health care cost trend rates on the service and interest cost components	142,000
Aggregate liability to participants	9,600,000	7,900,000
Current portion of postretirement liability	279,000	260,000	304,000
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%
Amount of discretionary awards made to participants	0	0	0
Aggregate liability to participants	$ 3,800,000	$ 3,800,000