Debt and Capital Lease Obligations (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Sep. 28, 2016
Long-term Debt	$ 267,028,000	$ 234,073,000
Long-term Debt, Excluding Current Maturities	267,002,000	234,033,000
Cash payments for interest	8,869,000	7,352,000	2,308,000
Loss on exchange of Senior Exchangeable Notes	0	0	1,012,000
Line of Credit Facility, Current Borrowing Capacity	300,000,000
Line of Credit Facility, Maximum Borrowing Capacity	350,000,000
Performance bonds under credit facility	19,100,000
Line of Credit Facility, Remaining Borrowing Capacity	163,900,000
Performance Bonds	22,300,000
Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	150,000,000
Long-term Debt	150,000,000	150,000,000
Line of Credit [Member]
Debt Instrument [Line Items]
Long-term Debt	117,000,000	84,000,000
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Long-term Debt	28,000	73,000
Short-term Debt [Member]
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	26,000	40,000
senior notes series a [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	75,000,000
Debt Instrument, Maturity Date	Sep. 30, 2021
Debt Instrument, Interest Rate, Effective Percentage	4.01%
Senior Notes Series B [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 75,000,000
Debt Instrument, Maturity Date	Sep. 30, 2023
Debt Instrument, Interest Rate, Effective Percentage	4.11%
Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.50%
Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.25%