Debt Level 4 (Details) (USD $)			3 Months Ended				3 Months Ended					3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Line of Credit [Member]	Dec. 31, 2012 Line of Credit [Member]	Mar. 31, 2013 Senior Notes [Member]	Dec. 31, 2012 Senior Notes [Member]	Mar. 31, 2013 senior notes series a [Member]	Mar. 31, 2013 Capital Lease Obligations [Member]	Dec. 31, 2012 Capital Lease Obligations [Member]	Mar. 31, 2013 Short-term Debt [Member]	Dec. 31, 2012 Short-term Debt [Member]	Mar. 31, 2013 Senior Notes Series B [Member]	Mar. 31, 2013 Minimum [Member]	Sep. 30, 2012 Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount					$ 150,000,000		$ 75,000,000					$ 75,000,000
Debt Instrument, Maturity Date			Sep. 28, 2016				Sep. 30, 2021					Sep. 30, 2023
Debt Instrument, Interest Rate, Effective Percentage							4.01%					4.11%
Line of Credit Facility, Current Borrowing Capacity	300,000,000
Line of Credit Facility, Maximum Borrowing Capacity	350,000,000
Debt Instrument, Basis Spread on Variable Rate													1.50%	2.25%
Performance bonds under credit facility	16,500,000
Line of Credit Facility, Remaining Borrowing Capacity	192,500,000
Performance Bonds	21,700,000
Long-term Debt	241,061,000	234,073,000	91,000,000	84,000,000	150,000,000	150,000,000		61,000	73,000
Long-term Debt, Current Maturities										39,000	40,000
Long-term Debt, Excluding Current Maturities	$ 241,022,000	$ 234,033,000