Financial Instruments (Schedule of Long-Term Debt) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Long-term debt	$ 319,153	$ 374,388
Less: current portion	(83,276)	(1,263)
Long-term debt, net of current portion	235,877	373,125
Convertible Notes [Member]
Debt Instrument [Line Items]
Long-term debt	28,261	27,228
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	132,000	187,000
Interest rate at end of period	3.92%	3.61%
Year of maturity	2015
Various Notes and Mortgages [Member]
Debt Instrument [Line Items]
Long-term debt	$ 8,892	$ 10,160
Interest rate at end of period	3.06%	3.05%
Maturity date range, end	Dec. 31, 2021