Financial Instruments (Schedule of Long-Term Debt) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term debt	$ 282,107	$ 272,111
Less: current portion	(50,015)	(50,015)
Long-term debt, net of current portion	232,092	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	182,000	172,000
Credit agreement, end of period interest rate	2.63%	2.69%
Year of maturity	2018
Various Notes and Mortgages [Member]
Debt Instrument [Line Items]
Long-term debt	$ 107	$ 111
Various notes and mortgages, average end of period rate	5.50%	5.50%
Maturity date range, end	Dec. 31, 2021