Debt Short-Term Borrowings (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Line of Credit Facility [Line Items]
Short-term borrowings	$ 66,342	$ 82,442
Short-term debt average amount outstanding	67,000	68,000
Weighted average interest rate	1.43%
Revolving Credit Facility
Line of Credit Facility [Line Items]
Short-term borrowings	66,342	82,442
Interest rate during the period	1.52%	1.58%
Minimum
Line of Credit Facility [Line Items]
Short-term borrowings	25,550	27,233
Maximum
Line of Credit Facility [Line Items]
Short-term borrowings	$ 111,912	$ 126,020