Debt Level 4 (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Debt Instrument [Line Items]
Loss on exchange of Senior Exchangeable Notes	$ 0	$ (210,000)	$ 0	$ (839,000)
Line of Credit Facility, Current Borrowing Capacity	300,000,000		300,000,000
Line of Credit Facility, Maximum Borrowing Capacity	350,000,000		350,000,000
Performance bonds under credit facility	16,000,000		16,000,000
Line of Credit Facility, Remaining Borrowing Capacity	228,000,000		228,000,000
Performance Bonds	24,900,000		24,900,000
Long-term Debt	206,676,000		206,676,000		225,419,000
Long-term Debt, Excluding Current Maturities	206,053,000		206,053,000		223,075,000
Line of Credit [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Sep. 28, 2016
Long-term Debt	56,000,000		56,000,000		73,000,000
Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	150,000,000		150,000,000
Long-term Debt	150,000,000		150,000,000		150,000,000
senior notes series a [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	75,000,000		75,000,000
Debt Instrument, Maturity Date	Sep. 30, 2021
Debt Instrument, Interest Rate, Effective Percentage	4.01%		4.01%
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Long-term Debt	102,000		102,000		132,000
Other Debt Obligations [Member]
Debt Instrument [Line Items]
Long-term Debt	574,000		574,000		2,287,000
Short-term Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	623,000		623,000		2,344,000
Senior Notes Series B [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 75,000,000		$ 75,000,000
Debt Instrument, Maturity Date	Sep. 30, 2023
Debt Instrument, Interest Rate, Effective Percentage	4.11%		4.11%
Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.50%		1.50%
Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.25%		2.25%