Pension, Savings and Postretirement Benefits (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 item	Dec. 31, 2011	Dec. 31, 2010
Fair value of plan assets
Balance at beginning of year	$ 19,609,000
Balance at end of year	22,372,000
Components of cost recognized in the statement of operations
Curtailment of hourly plan	(1,325,000)
Pension plans
Pension, savings and postretirement benefits
Number of noncontributory plans	2
Projected benefit obligation
Balance at beginning of year	25,590,000	21,284,000
Service cost	455,000	287,000	361,000
Interest cost	1,141,000	1,090,000	1,123,000
Plan amendments	951,000
Actuarial loss	1,766,000	3,633,000
Benefits paid	(735,000)	(704,000)
Balance at end of year	29,168,000	25,590,000	21,284,000
Fair value of plan assets
Balance at beginning of year	19,609,000	19,328,000
Employer contributions	1,500,000	1,293,000
Actual return on plan assets	1,998,000	(308,000)
Benefits paid	(735,000)	(704,000)
Balance at end of year	22,372,000	19,609,000	19,328,000
Unfunded benefit obligation
Unfunded benefit obligation at end of year	(6,796,000)	(5,981,000)
Additional benefits accrued after effective date of the freeze of plan	0
Components of cost recognized in the statement of operations
Service cost	455,000	287,000	361,000
Interest cost	1,141,000	1,090,000	1,123,000
Expected return on assets	(1,641,000)	(1,549,000)	(1,389,000)
Curtailment of hourly plan	1,325,000
Amortization of unrecognized prior service costs	244,000	170,000	170,000
Amortization of unrecognized loss	813,000	495,000	358,000
Net periodic cost (income)	2,337,000	493,000	623,000
Hourly Plan
Projected benefit obligation
Balance at end of year	20,474,000	17,775,000
Fair value of plan assets
Balance at end of year	15,602,000	13,687,000
Unfunded benefit obligation
Unfunded benefit obligation at end of year	(4,872,000)	(4,088,000)
Salaried Plan
Projected benefit obligation
Balance at end of year	8,694,000	7,815,000
Fair value of plan assets
Balance at end of year	6,770,000	5,922,000
Unfunded benefit obligation
Unfunded benefit obligation at end of year	(1,924,000)	(1,893,000)
Postretirement health cost coverage
Pension, savings and postretirement benefits
Monthly maximum contribution to the cost of providing retiree health care benefits (in dollars per employee)	250
Projected benefit obligation
Balance at beginning of year	12,524,000	11,968,000
Service cost	256,000	179,000	201,000
Interest cost	527,000	573,000	612,000
Actuarial loss	1,286,000	274,000
Benefits paid	(502,000)	(470,000)
Balance at end of year	14,091,000	12,524,000	11,968,000
Fair value of plan assets
Employer contributions	502,000	471,000
Benefits paid	(502,000)	(470,000)
Unfunded benefit obligation
Unfunded benefit obligation at end of year	(14,091,000)	(12,524,000)
Components of cost recognized in the statement of operations
Service cost	256,000	179,000	201,000
Interest cost	527,000	573,000	612,000
Amortization of unrecognized prior service costs	(172,000)	(172,000)	(212,000)
Amortization of unrecognized loss	208,000	70,000	91,000
Effect of curtailments and settlements			(714,000)
Net periodic cost (income)	$ 819,000	$ 650,000	$ (22,000)