Short-term Debt and Credit Lines - Schedule of Short-Term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Short-term Debt
Total short-term debt	$ 37,950	$ 71,360
Notes payable to banks
Short-term Debt
Total short-term debt	8,200	5,860
Commercial paper
Short-term Debt
Total short-term debt	$ 29,750	$ 65,500