Debt (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Debt Instrument [Line Items]
Borrowings under short-term line of credit	$ 27,000	$ 0	$ 50,000
Long-term debt
Total current maturities of long-term debt	89,387	51,998	45,096
Total long-term debt, less current maturities	300,220	375,213	409,020
Nonrecourse
Debt Instrument [Line Items]
Borrowings under short-term line of credit	0	0	0
Long-term debt
Total current maturities of long-term debt	3,100	6,012	3,274
Total long-term debt, less current maturities	2,515	4,063	19,621
Recourse
Debt Instrument [Line Items]
Borrowings under short-term line of credit	27,000	0	50,000
Long-term debt
Total current maturities of long-term debt	86,287	45,986	41,822
Total long-term debt, less current maturities	$ 297,705	$ 371,150	$ 389,399