Financial Instruments (Schedule of Long-Term Debt) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			1 Months Ended	12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Oct. 31, 2013 Private Placement, Notes [Member]	Dec. 31, 2013 Private Placement, Notes [Member]	Dec. 31, 2012 Private Placement, Notes [Member]	Dec. 31, 2013 Credit Agreement [Member]	Dec. 31, 2012 Credit Agreement [Member]	Dec. 31, 2013 Convertible Notes [Member]	Dec. 31, 2012 Convertible Notes [Member]	Dec. 31, 2013 Various Notes and Mortgages [Member]	Dec. 31, 2012 Various Notes and Mortgages [Member]
Debt Instrument [Line Items]
Long-term debt	$ 303,875	$ 319,153			$ 100,000	$ 150,000	$ 200,000	$ 132,000		$ 28,261	$ 3,875	$ 8,892
Less: current portion	(3,764)	(83,276)
Long-term debt, net of current portion	300,111	235,877
Debt issued					150,000					28,437
Interest rate					6.84%				2.25%
Interest rate at end of period							2.53%	3.92%			3.10%	3.06%
Maturity date					Oct. 25, 2017
Year of maturity							2018		2026
Maturity date range, start					Jan. 01, 2015
Maturity date range, end					Dec. 31, 2017						Dec. 31, 2021
Repayments of debt	$ 132,691	$ 102,128	$ 65,575	$ 50,000