Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Debt Instrument [Line Items]
Short-term debt	$ 19,000	$ 29,000	$ 0
Long-term debt
Total current maturities of long-term debt	53,972	47,545	51,520
Total long-term debt, less current maturities	371,315	397,065	395,559
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	19,000	29,000	0
Long-term debt
Total current maturities of long-term debt	53,972	47,545	51,520
Total long-term debt, less current maturities	$ 371,315	$ 397,065	$ 395,559