Financial Instruments (Schedule of Long-Term Debt) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt	$ 255,092	$ 265,096
Less: current portion	(16)	(16)
Long-term debt, net of current portion	255,076	265,080
Private Placement, Notes [Member]
Debt Instrument [Line Items]
Long-term debt	$ 50,000	$ 50,000
Interest rate	6.84%	6.84%
Maturity date range, end	Dec. 31, 2017
Revolving Credit Agreement [Member]
Debt Instrument [Line Items]
Long-term debt	$ 205,000	$ 215,000
Interest rate at end of period	2.34%	2.27%
Various Notes and Mortgages [Member]
Debt Instrument [Line Items]
Long-term debt	$ 92	$ 96
Interest rate at end of period	5.50%	5.50%
Maturity date range, end	Dec. 31, 2021