Financial Instruments (Schedule of Long-Term Debt) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term debt	$ 265,096	$ 272,111
Less: current portion	(16)	(50,015)
Long-term debt, net of current portion	265,080	222,096
Private Placement, Notes [Member]
Debt Instrument [Line Items]
Long-term debt	$ 50,000	100,000
Interest rate	6.84%
Maturity date range, end	Dec. 31, 2017
Revolving Credit Agreement [Member]
Debt Instrument [Line Items]
Long-term debt	$ 215,000	$ 172,000
Interest rate at end of period	2.27%	2.69%
Year of maturity	2020
Various Notes and Mortgages [Member]
Debt Instrument [Line Items]
Long-term debt	$ 96	$ 111
Interest rate at end of period	5.50%	5.50%
Maturity date range, end	Dec. 31, 2021