Short-term Debt and Credit Lines (Total Short-term Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Short-term Debt
Total short-term debt	$ 71,360	$ 75,927
Notes payable to banks
Short-term Debt
Total short-term debt	5,860	5,977
Commercial paper
Short-term Debt
Total short-term debt	$ 65,500	$ 69,950