Debt Level 4 (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Debt Instrument [Line Items]
Loss on exchange of Senior Exchangeable Notes	$ 0	$ (31,000)	$ 0	$ (870,000)
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	17,000,000		17,000,000
Line of Credit Facility, Remaining Borrowing Capacity	220,000,000		220,000,000
Performance Bonds	26,400,000		26,400,000
Long-term Debt	213,089,000		213,089,000		225,419,000
Long-term Debt, Excluding Current Maturities	213,044,000		213,044,000		223,075,000
Line of Credit [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Sep. 28, 2016
Long-term Debt	63,000,000		63,000,000		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	89,000		89,000		132,000
Other Debt Obligations [Member]
Debt Instrument [Line Items]
Long-term Debt	0		0		2,287,000
Short-term Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	45,000		45,000		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%