Financial Instruments (Schedule of Long-Term Debt) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Long-term debt	$ 301,622	$ 303,875
Less: current portion	(2,514)	(3,764)
Long-term debt, net of current portion	299,108	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	199,000	200,000
Interest rate at end of period	2.53%	2.53%
Year of maturity	2018
Various Notes and Mortgages [Member]
Debt Instrument [Line Items]
Long-term debt	$ 2,622	$ 3,875
Interest rate at end of period	3.14%	3.10%
Maturity date range, end	Dec. 31, 2021