Debt (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Debt Instrument [Line Items]
Borrowings under short-term line of credit	$ 275,522	$ 71,500	$ 105,000
Long-term debt
Total current maturities of long-term debt	32,655	32,208	45,171
Total long-term debt, less current maturities	312,404	238,885	235,729
Nonrecourse
Debt Instrument [Line Items]
Borrowings under short-term line of credit	522	0	0
Long-term debt
Total current maturities of long-term debt	1,716	157	2,806
Total long-term debt, less current maturities	25,686	797	6,971
Recourse
Debt Instrument [Line Items]
Borrowings under short-term line of credit	275,000	71,500	105,000
Long-term debt
Total current maturities of long-term debt	30,939	32,051	42,365
Total long-term debt, less current maturities	$ 286,718	$ 238,088	$ 228,758