Long-Term Debt (Details) (USD $)	3 Months Ended
	Jun. 30, 2012	Mar. 31, 2012	Apr. 02, 2011	Apr. 03, 2012	Dec. 31, 2011
Long-Term Debt [Abstract]
Credit facility		$ 145,000,000			$ 155,000,000
Exchangeable unsecured notes, due 2102		95,042,000			95,042,000
Long-term Debt		389,486,000			399,054,000
Less current portion		0			0
Long-term debt, less current portion		389,486,000			399,054,000
Debt Instrument [Line Items]
Non-cash amortization of debt discount		611,000	376,000
Line of Credit Facility, Maximum Borrowing Capacity		450,000,000		528,000,000
Line of Credit Facility, Amendment Fee Amount	390,000
Convertible Senior Debentures 2040 [Member]
Long-Term Debt [Abstract]
Convertible senior debentures		98,766,000			98,463,000
Debt Instrument [Line Items]
Convertible senior debentures issuance date		November 9, 2010
Principal amount of convertible senior debentures		275,000,000			275,000,000
Principal amount of the debentures		275,000,000			275,000,000
Unamortized discount		(176,724,000)			(177,131,000)
Embedded derivative		490,000			594,000
Carrying value of liability component		98,766,000			98,463,000
Equity component - net carrying value		110,094,000			110,094,000
Stated rate of interest on convertible senior debentures (in hundredths)		2.25%
Effective rate of interest on convertible senior debentures (in hundredths)		8.00%
Contractual coupon interest		1,547,000	1,547,000
Non-cash amortization of debt discount		407,000	376,000
Non-cash amortization of deferred financing costs		22,000	22,000
Non-cash change in value of derivative liability		(104,000)	(61,000)
Total interest expense related to the debentures		1,872,000	1,884,000
Convertible Senior Debentures 2041 [Member]
Long-Term Debt [Abstract]
Convertible senior debentures		50,678,000			50,549,000
Debt Instrument [Line Items]
Convertible senior debentures issuance date		May 13, 2011
Principal amount of convertible senior debentures		150,000,000			150,000,000
Principal amount of the debentures		150,000,000			150,000,000
Unamortized discount		(99,639,000)			(99,843,000)
Embedded derivative		317,000			392,000
Carrying value of liability component		50,678,000			50,549,000
Equity component - net carrying value		62,246,000			62,246,000
Stated rate of interest on convertible senior debentures (in hundredths)		2.25%
Effective rate of interest on convertible senior debentures (in hundredths)		8.375%
Contractual coupon interest		844,000
Non-cash amortization of debt discount		204,000
Non-cash amortization of deferred financing costs		12,000
Non-cash change in value of derivative liability		(75,000)
Total interest expense related to the debentures		985,000
Debt instrument percentage of conversion price (in hundredths)		130.00%
Debt instrument, conversion price amount		24.73
Debt instrument, Percentage of sale price of common stock (in hundredths)		98.00%
Debt instrument, initial conversion shares of common stock		52.5659
Debt instrument, principal amount of debentures		$ 1,000
Debt instrument, initial conversion price (in dollars per share)		$ 19.02
Debt instrument, percentage of initial conversion price premium (in hundredths)		12.50%
Debt instrument, conversion price (in dollars per share)		$ 16.91