Long-Term Debt (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 27, 2014	Sep. 28, 2013	Sep. 27, 2014	Sep. 28, 2013	Dec. 31, 2013
Debt Instrument [Line Items]
Long-term debt	$ 440,880,000		$ 440,880,000		$ 364,911,000
Exchangeable unsecured notes, due 2102	38,642,000		38,642,000		38,642,000
Credit facility	187,000,000		187,000,000		114,000,000
Less current portion	0		0		0
Long-term debt, less current portion	440,880,000		440,880,000		364,911,000
Debt Instruments [Abstract]
Principal amount of debt	575,000,000		575,000,000		575,000,000
Debt instrument percentage of conversion price (in hundredths)			130.00%
Debt instrument, Percentage of sale price of common stock (in hundredths)	98.00%		98.00%
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	575,000,000		575,000,000		575,000,000
Unamortized discount	(360,838,000)		(360,838,000)		(363,768,000)
Embedded derivative	1,076,000		1,076,000		1,037,000
Carrying value of liability component	215,238,000		215,238,000		212,269,000
Equity component - net carrying value	230,214,000		230,214,000		230,214,000
Interest expense related to debentures [Abstract]
Contractual coupon interest	3,235,000	3,235,000	9,705,000	9,705,000
Non-cash amortization of debt discount	997,000	922,000	2,930,000	2,709,000
Non-cash amortization of deferred financing costs	46,000	46,000	141,000	141,000
Non-cash change in value of derivative liability	77,000	(40,000)	39,000	(366,000)
Total interest expense related to the debentures	4,355,000	4,163,000	12,815,000	12,189,000
Convertible Senior Debentures 2040 [Member]
Debt Instrument [Line Items]
Convertible Debt, Noncurrent	103,364,000		103,364,000		101,846,000
Debt Instruments [Abstract]
Issuance date			Nov. 09, 2010
Debt maturity date			Nov. 15, 2040
Principal amount of debt	275,000,000		275,000,000		275,000,000
Stated rate of interest on debt (in hundredths)	2.25%		2.25%
Effective rate of interest on convertible senior debentures (in hundredths)	8.00%		8.00%
Debt Instrument, Convertible, Stock Price Trigger			$ 17.84
Debt conversion rate	72.8961
Debt effective conversion price	$ 13.72		$ 13.72
Convertible senior debentures call date	Nov. 20, 2020
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	275,000,000		275,000,000		275,000,000
Unamortized discount	(172,189,000)		(172,189,000)		(173,645,000)
Embedded derivative	553,000		553,000		491,000
Carrying value of liability component	103,364,000		103,364,000		101,846,000
Equity component - net carrying value	110,094,000		110,094,000		110,094,000
Interest expense related to debentures [Abstract]
Contractual coupon interest	1,547,000	1,547,000	4,641,000	4,641,000
Non-cash amortization of debt discount	495,000	458,000	1,456,000	1,346,000
Non-cash amortization of deferred financing costs	22,000	22,000	66,000	66,000
Non-cash change in value of derivative liability	93,000	(30,000)	62,000	(193,000)
Total interest expense related to the debentures	2,157,000	1,997,000	6,225,000	5,860,000
Convertible Senior Debentures 2041 [Member]
Debt Instrument [Line Items]
Convertible Debt, Noncurrent	52,966,000		52,966,000		52,264,000
Debt Instruments [Abstract]
Issuance date			May 13, 2011
Debt maturity date			May 15, 2041
Principal amount of debt	150,000,000		150,000,000		150,000,000
Stated rate of interest on debt (in hundredths)	2.25%		2.25%
Effective rate of interest on convertible senior debentures (in hundredths)	8.375%		8.375%
Debt Instrument, Convertible, Stock Price Trigger			$ 24.44
Debt conversion rate	53.1957
Debt effective conversion price	$ 18.80		$ 18.80
Convertible senior debentures call date	May 20, 2021
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	150,000,000		150,000,000		150,000,000
Unamortized discount	(97,348,000)		(97,348,000)		(98,085,000)
Embedded derivative	314,000		314,000		349,000
Carrying value of liability component	52,966,000		52,966,000		52,264,000
Equity component - net carrying value	62,246,000		62,246,000		62,246,000
Interest expense related to debentures [Abstract]
Contractual coupon interest	844,000	844,000	2,532,000	2,532,000
Non-cash amortization of debt discount	251,000	231,000	737,000	679,000
Non-cash amortization of deferred financing costs	11,000	11,000	35,000	35,000
Non-cash change in value of derivative liability	(29,000)	(13,000)	(35,000)	(100,000)
Total interest expense related to the debentures	1,077,000	1,073,000	3,269,000	3,146,000
Convertible Senior Debentures 2042 [Member]
Debt Instrument [Line Items]
Convertible Debt, Noncurrent	58,908,000		58,908,000		58,159,000
Debt Instruments [Abstract]
Issuance date			May 31, 2012
Debt maturity date			Jun. 01, 2042
Principal amount of debt	150,000,000		150,000,000		150,000,000
Stated rate of interest on debt (in hundredths)	2.25%		2.25%
Effective rate of interest on convertible senior debentures (in hundredths)	7.50%		7.50%
Debt Instrument, Convertible, Stock Price Trigger			$ 15.17
Debt conversion rate	85.7084
Debt effective conversion price	$ 11.67		$ 11.67
Convertible senior debentures call date	Jun. 07, 2022
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	150,000,000		150,000,000		150,000,000
Unamortized discount	(91,301,000)		(91,301,000)		(92,038,000)
Embedded derivative	209,000		209,000		197,000
Carrying value of liability component	58,908,000		58,908,000		58,159,000
Equity component - net carrying value	57,874,000		57,874,000		57,874,000
Interest expense related to debentures [Abstract]
Contractual coupon interest	844,000	844,000	2,532,000	2,532,000
Non-cash amortization of debt discount	251,000	233,000	737,000	684,000
Non-cash amortization of deferred financing costs	13,000	13,000	40,000	40,000
Non-cash change in value of derivative liability	13,000	3,000	12,000	(73,000)
Total interest expense related to the debentures	$ 1,121,000	$ 1,093,000	$ 3,321,000	$ 3,183,000