Employee Retirement Plans (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension benefits
Assumptions used in determining net periodic pension cost for the plans
Discount rates (as a percent)	4.60%	5.50%	6.00%
Rates of increase in compensation levels: Salaried (as a percent)	3.50%	3.50%	3.50%
Expected long-term rate of return on assets (as a percent)	7.25%	8.00%	8.00%
Expected long-term rate of return on plan assets for the next fiscal year	0.0725
Assumptions used to determine the benefit obligation
Discount rate (as a percent)	4.10%	4.60%
Expected benefit payments
2013	$ 1,330
2014	1,340
2015	1,360
2016	1,380
2017	1,410
2018-2021	8,010
Required pension funding contributions made	2,014	1,917
Amounts included in other comprehensive loss, net of tax
Net actuarial gain (loss)	(7,803)
Amounts that will be amortized from accumulated other comprehensive income loss into net periodic pension or OPEB cost in the next fiscal year
Estimated actuarial gain (loss)	(1,204)
Pension benefits | Minimum
Expected benefit payments
Required pension funding contributions made	2,014
Required pension funding contributions expected to be made in next fiscal year	831
Postretirement benefits
Assumptions used in determining net periodic pension cost for the plans
Discount rates (as a percent)	4.40%	5.50%	6.00%
Summary of healthcare cost trend rates
Immediate healthcare cost trend rate (as a percent)	8.00%	9.00%	9.00%
Ultimate healthcare cost trend rate (as a percent)	4.50%	5.00%	5.00%
Assumed annual reduction in trend rate (as a percent)			0.50%
Participation (as a percent)	80.00%	80.00%	80.00%
Assumed health care cost trend rate for the next fiscal year (as a percent)		8.00%
Ultimate rate in 2019 (as a percent)		4.50%
Assumptions used to determine the benefit obligation
Discount rate (as a percent)	3.70%	4.40%
Effect of one percentage point change in the healthcare cost trend rate
Effect on total service and interest cost, 1% increase	71
Effect on total service and interest cost, 1% decrease	(61)
Effect on postretirement benefit obligation, 1% increase	808
Effect on postretirement benefit obligation, 1% decrease	(696)
Amounts included in other comprehensive loss, net of tax
Net actuarial gain (loss)	1,063
Amounts that will be amortized from accumulated other comprehensive income loss into net periodic pension or OPEB cost in the next fiscal year
Estimated actuarial gain (loss)	$ 172
Postretirement benefits | Under 65
Summary of healthcare cost trend rates
Assumed health care cost trend rate for the next fiscal year (as a percent)	8.00%
Ultimate rate in 2021 (as a percent)	4.50%
Age of participants	65
Postretirement benefits | Over 65
Summary of healthcare cost trend rates
Assumed health care cost trend rate for the next fiscal year (as a percent)	6.00%
Ultimate rate in 2021 (as a percent)	4.50%
Age of participants	65