Debt Short-Term Borrowings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Line of Credit Facility [Line Items]
Short-term borrowings	$ 140,465	$ 104,978
Short-term debt average amount outstanding	$ 185,000	119,000
Weighted average interest rate	1.83%
Revolving Credit Facility
Line of Credit Facility [Line Items]
Short-term borrowings		$ 104,978
Interest rate during the period	1.52%	1.31%
Minimum
Line of Credit Facility [Line Items]
Short-term borrowings	$ 105,014	$ 35,981
Maximum
Line of Credit Facility [Line Items]
Short-term borrowings	$ 311,506	$ 184,188