Employee Retirement Plans (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Amounts recognized in the consolidated balance sheets consisted
Retiree health benefit obligation	$ 6,541	$ 8,053
Amount recognized in accumulated other comprehensive loss
Reduction to the net actuarial loss recognized			326
Pension benefits
Change in projected benefit obligation:
Benefit obligation at beginning of year	32,800	28,557
Service cost	268	961	800
Interest cost	1,482	1,539	1,432
Actuarial loss	2,944	4,126
Benefits paid	(1,285)	(975)
Effect of curtailment		(1,408)
Benefit obligation at end of year	36,209	32,800	28,557
Change in plan assets:
Fair value of plan assets at beginning of year	18,637	17,804
Actual return on plan assets	2,442	(109)
Employer contributions through December 31	2,014	1,917
Benefits paid	(1,285)	(975)
Fair value of plan assets at end of year	21,808	18,637	17,804
Funded Status: accrued pension liability	(14,401)	(14,163)
Salaried Pension Plan
Threshold period of service considered for freezing benefits	5 years
Benefit accrual as a percentage of pay	1.67%
Reduced benefit accrual as a percentage of pay	1.00%
Amount recognized in accumulated other comprehensive loss
Reduction to the net actuarial loss recognized		1,408
Components of net periodic cost:
Service cost	268	961	800
Interest cost	1,482	1,539	1,432
Expected return on plan assets	(1,274)	(1,357)	(1,162)
Amortization of net (gain) loss	770	454	324
Net periodic cost	1,246	1,597	1,394
Accumulated benefit obligation	34,949	31,322
Pension benefits | Minimum
Change in plan assets:
Employer contributions through December 31	2,014
Postretirement benefits
Change in projected benefit obligation:
Benefit obligation at beginning of year	8,402	7,576
Service cost	281	263	308
Interest cost	360	407	455
Participant contributions	103	95
Actuarial loss	(1,590)	426
Benefits paid	(744)	(365)
Effect of curtailment			1,031
Benefit obligation at end of year	6,812	8,402	7,576
Change in plan assets:
Benefits paid	(744)	(365)
Amounts recognized in the consolidated balance sheets consisted
Accrued expenses and other current liabilities	271	349
Retiree health benefit obligation	6,541	8,053
Amounts recognized in the consolidated balance sheets consisted	6,812	8,402
Amount recognized in accumulated other comprehensive loss
Reduction to the net actuarial loss recognized			364
Components of net periodic cost:
Service cost	281	263	308
Interest cost	360	407	455
Amortization of net (gain) loss	(17)	(61)	(6)
Curtailment gain			(667)
Net periodic cost	$ 624	$ 609	$ 90
Postretirement benefits | Minimum
Employee retirement plans
Period of service of employees	12 years
Postretirement benefits | Maximum
Employee retirement plans
Period of coverage under the plan	10 years