Debt (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Debt Instrument [Line Items]
Borrowings under short-term line of credit	$ 226,100	$ 0	$ 292,100
Long-term debt
Total current maturities of long-term debt	90,760	51,998	43,052
Total long-term debt, less current maturities	306,161	375,213	412,700
Nonrecourse
Debt Instrument [Line Items]
Borrowings under short-term line of credit	0	0	8,400
Long-term debt
Total current maturities of long-term debt	6,012	6,012	3,271
Total long-term debt, less current maturities	3,288	4,063	24,141
Recourse
Debt Instrument [Line Items]
Borrowings under short-term line of credit	226,100	0	283,700
Long-term debt
Total current maturities of long-term debt	84,748	45,986	39,781
Total long-term debt, less current maturities	$ 302,873	$ 371,150	$ 388,559