Long-Term Debt (Details) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 03, 2015 USD ($) $ / shares	Sep. 27, 2014 USD ($)	Oct. 03, 2015 USD ($) $ / shares	Sep. 27, 2014 USD ($)	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Long-term debt	$ 431,766		$ 431,766		$ 454,922
Exchangeable unsecured notes, due 2102	38,642		38,642		38,642
Credit facility	173,000		173,000		200,000
Less current portion	0		0		0
Long-term debt, less current portion	431,766		431,766		454,922
Debt Instruments [Abstract]
Principal amount of debt	$ 575,000		$ 575,000		575,000
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		$ 575,000		575,000
Unamortized discount	(356,658)		(356,658)		(359,825)
Embedded derivative	1,782		1,782		1,105
Carrying value of liability component	220,124		220,124		216,280
Equity component - net carrying value	230,214		230,214		230,214
Interest expense related to debentures [Abstract]
Contractual coupon interest	3,235	$ 3,235	9,705	$ 9,705
Non-cash amortization of debt discount	1,077	997	3,167	2,930
Non-cash amortization of deferred financing costs	47	46	142	141
Non-cash change in value of derivative liability	395	77	677	39
Total interest expense related to the debentures	4,754	4,355	13,691	12,815
Convertible Senior Debentures, Due 2040 [Member]
Debt Instrument [Line Items]
Convertible Debt, Noncurrent	105,719		$ 105,719		103,841
Debt Instruments [Abstract]
Issuance date			Nov. 09, 2010
Debt maturity date			Nov. 15, 2040
Principal amount of debt	$ 275,000		$ 275,000		275,000
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 | $ / shares			$ 17.49
Debt conversion rate	74.3326
Debt effective conversion price | $ / shares	$ 13.45		$ 13.45
Convertible senior debentures call date	Nov. 20, 2020
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	$ 275,000		$ 275,000		275,000
Unamortized discount	(170,111)		(170,111)		(171,685)
Embedded derivative	830		830		526
Carrying value of liability component	105,719		105,719		103,841
Equity component - net carrying value	110,094		110,094		110,094
Interest expense related to debentures [Abstract]
Contractual coupon interest	1,547	1,547	4,641	4,641
Non-cash amortization of debt discount	535	495	1,574	1,456
Non-cash amortization of deferred financing costs	22	22	66	66
Non-cash change in value of derivative liability	198	93	304	62
Total interest expense related to the debentures	2,302	2,157	6,585	6,225
Convertible Senior Debentures, Due 2041 [Member]
Debt Instrument [Line Items]
Convertible Debt, Noncurrent	54,278		$ 54,278		53,249
Debt Instruments [Abstract]
Issuance date			May 13, 2011
Debt maturity date			May 15, 2041
Principal amount of debt	$ 150,000		$ 150,000		150,000
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 | $ / shares			$ 23.97
Debt conversion rate	54.2441
Debt effective conversion price | $ / shares	$ 18.44		$ 18.44
Convertible senior debentures call date	May 20, 2021
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	$ 150,000		$ 150,000		150,000
Unamortized discount	(96,292)		(96,292)		(97,092)
Embedded derivative	570		570		341
Carrying value of liability component	54,278		54,278		53,249
Equity component - net carrying value	62,246		62,246		62,246
Interest expense related to debentures [Abstract]
Contractual coupon interest	844	844	2,532	2,532
Non-cash amortization of debt discount	272	251	800	737
Non-cash amortization of deferred financing costs	12	11	36	35
Non-cash change in value of derivative liability	92	(29)	229	(35)
Total interest expense related to the debentures	1,220	1,077	3,597	3,269
Convertible Senior Debentures, Due 2042 [Member]
Debt Instrument [Line Items]
Convertible Debt, Noncurrent	60,127		$ 60,127		59,190
Debt Instruments [Abstract]
Issuance date			May 31, 2012
Debt maturity date			Jun. 01, 2042
Principal amount of debt	$ 150,000		$ 150,000		150,000
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 | $ / shares			$ 14.87
Debt conversion rate	87.3974
Debt effective conversion price | $ / shares	$ 11.44		$ 11.44
Convertible senior debentures call date	Jun. 07, 2022
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	$ 150,000		$ 150,000		150,000
Unamortized discount	(90,255)		(90,255)		(91,048)
Embedded derivative	382		382		238
Carrying value of liability component	60,127		60,127		59,190
Equity component - net carrying value	57,874		57,874		$ 57,874
Interest expense related to debentures [Abstract]
Contractual coupon interest	844	844	2,532	2,532
Non-cash amortization of debt discount	270	251	793	737
Non-cash amortization of deferred financing costs	13	13	40	40
Non-cash change in value of derivative liability	105	13	144	12
Total interest expense related to the debentures	$ 1,232	$ 1,121	$ 3,509	$ 3,321