Financial Instruments (Schedule of Long-Term Debt) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Long-term debt	$ 333,636	$ 319,153
Less: current portion	(55,014)	(83,276)
Long-term debt, net of current portion	278,622	235,877
Convertible Notes [Member]
Debt Instrument [Line Items]
Long-term debt		28,261
Debt issued	28,437
Interest rate	2.25%
Year of maturity	2026
Private Placement, Notes [Member]
Debt Instrument [Line Items]
Long-term debt	150,000	150,000
Debt issued	150,000
Interest rate	6.84%
Maturity date	Oct. 25, 2017
Maturity date range, start	Jan. 01, 2013
Maturity date range, end	Dec. 31, 2017
Credit Agreement [Member]
Debt Instrument [Line Items]
Long-term debt	176,000	132,000
Interest rate at end of period	2.68%	3.92%
Year of maturity	2018
Various Notes and Mortgages [Member]
Debt Instrument [Line Items]
Long-term debt	$ 7,636	$ 8,892
Interest rate at end of period	3.06%	3.06%
Maturity date range, end	Dec. 31, 2021