Financial Instruments (Schedule of Long-Term Debt) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Long-term debt	$ 284,369	$ 303,875
Less: current portion	(1,265)	(3,764)
Long-term debt, net of current portion	283,104	300,111
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	183,000	200,000
Credit agreement, end of period interest rate	2.62%	2.53%
Year of maturity	2018
Various Notes and Mortgages [Member]
Debt Instrument [Line Items]
Long-term debt	$ 1,369	$ 3,875
Various notes and mortgages, average end of period rate	3.13%	3.10%
Maturity date range, end	Dec. 31, 2021