Retirement Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of year	$ 159,791,000
Employer Contributions	26,000,000	20,000,000
Fair value of plan assets at end of year	173,422,000	159,791,000
Pension Plan
Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of year	159,791,000	133,554,000
Actual return on plan assets	(2,481,000)	14,477,000
Employer Contributions	26,000,000	20,000,000
Gross benefits paid	(9,888,000)	(8,240,000)
Fair value of plan assets at end of year	173,422,000	159,791,000	133,554,000
Change in Benefit Obligation
Net benefit obligation at beginning of year	129,114,000	119,935,000
Service cost	9,898,000	9,622,000	8,649,000
Interest cost	6,414,000	6,377,000	6,262,000
Actuarial loss	1,308,000	1,420,000
Gross benefits paid	(9,888,000)	(8,240,000)
Net benefit obligation at end of year	136,846,000	129,114,000	119,935,000
Funded (unfunded) status	36,576,000	30,677,000
Noncurrent assets	39,802,000	31,274,000
Current liabilities	0	0
Noncurrent liabilities	(3,226,000)	(597,000)
Asset (Liability) Recognized in the Consolidated Balance Sheet	36,576,000	30,677,000
Defined Benefit Plan Amortization Of Gains Losses in Next Fiscal Year	3,000,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit in Next Fiscal Year	100,000
Postretirement Plan
Change in Fair Value of Plan Assets
Employer Contributions	502,000	610,000
Gross benefits paid	(502,000)	(610,000)
Change in Benefit Obligation
Net benefit obligation at beginning of year	4,150,000	4,429,000
Service cost	0	0
Interest cost	198,000	227,000	261,000
Actuarial loss	123,000	104,000
Gross benefits paid	(502,000)	(610,000)
Net benefit obligation at end of year	3,969,000	4,150,000	4,429,000
Funded (unfunded) status	(3,969,000)	(4,150,000)
Noncurrent assets	0	0
Current liabilities	(495,000)	(587,000)
Noncurrent liabilities	(3,474,000)	(3,563,000)
Asset (Liability) Recognized in the Consolidated Balance Sheet	(3,969,000)	(4,150,000)
Defined Benefit Plan Amortization Of Prior Service Cost Credit in Next Fiscal Year	$ 200,000