Financial Instruments (Schedule of Long-Term Debt) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term debt	$ 270,100	$ 272,111
Less: current portion	(50,016)	(50,015)
Long-term debt, net of current portion	220,084	222,096
Private Placement, Notes [Member]
Debt Instrument [Line Items]
Long-term debt	$ 100,000	100,000
Interest rate	6.84%
Maturity date	Oct. 25, 2017
Maturity date range, start	Jan. 01, 2015
Maturity date range, end	Dec. 31, 2017
Credit Agreement [Member]
Debt Instrument [Line Items]
Long-term debt	$ 170,000	$ 172,000
Credit agreement, end of period interest rate	2.36%	2.69%
Maturity date	Dec. 31, 2020
Various Notes and Mortgages [Member]
Debt Instrument [Line Items]
Long-term debt	$ 100	$ 111
Various notes and mortgages, average end of period rate	5.50%	5.50%
Maturity date range, end	Dec. 31, 2021