Debt (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011
Debt Instrument [Line Items]
Borrowings under short-term line of credit	$ 309,608	$ 71,500	$ 194,200
Long-term debt
Total current maturities of long-term debt	29,647	32,208	45,432
Total long-term debt, less current maturities	317,648	238,885	260,645
Nonrecourse
Debt Instrument [Line Items]
Borrowings under short-term line of credit	1,608	0	0
Long-term debt
Total current maturities of long-term debt	1,385	157	2,827
Total long-term debt, less current maturities	32,544	797	11,690
Recourse
Debt Instrument [Line Items]
Borrowings under short-term line of credit	308,000	71,500	194,200
Long-term debt
Total current maturities of long-term debt	28,262	32,051	42,605
Total long-term debt, less current maturities	$ 285,104	$ 238,088	$ 248,955