Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Debt Instrument [Line Items]
Short-term debt	$ 124,000	$ 29,000	$ 179,404
Long-term debt
Total current maturities of long-term debt	62,482	47,545	53,720
Total long-term debt, less current maturities	354,066	397,065	398,746
Nonrecourse
Debt Instrument [Line Items]
Short-term debt	0	0	0
Long-term debt
Total current maturities of long-term debt	0	0	0
Total long-term debt, less current maturities	0	0	0
Recourse
Debt Instrument [Line Items]
Short-term debt	124,000	29,000	179,404
Long-term debt
Total current maturities of long-term debt	62,482	47,545	53,720
Total long-term debt, less current maturities	$ 354,066	$ 397,065	$ 398,746