Short-Term Borrowings and Credit Arrangements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Commercial Paper, Balance	$ 300,811	$ 229,874
Maximum aggregate amount issuable at any time under commercial paper program	$ 340,000
Short term borrowings maximum days outstanding	270
Short-term Debt [Member]
Short-term Debt [Line Items]
Commercial Paper, Balance	$ 300,800	$ 229,900
Commercial Paper, Interest Rate	1.07%	0.82%
Maximum short-term debt outstanding	$ 300,800	$ 267,800
Average short-term debt outstanding	$ 210,700	$ 192,800
Weighted average interest rate	0.86%	0.61%