Long-Term Debt (Details) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 01, 2017 USD ($) $ / shares	Jul. 02, 2016 USD ($)	Jul. 01, 2017 USD ($) $ / shares	Jul. 02, 2016 USD ($)	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Credit facility	$ 133,000		$ 133,000		$ 143,000
Deferred Financing Costs	(9,990)		(9,990)		(10,880)
Long-term debt	350,329		350,329		357,023
Less current portion	0		0		0
Long-term debt, less current portion	350,329		350,329		357,023
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%
Principal payments on long-term debt and capital leases			$ 0	$ (34,044)
Liability and equity components of convertible debentures [Abstract]
Principal amount of the debentures	$ 575,000		575,000		575,000
Unamortized discount	(348,507)		(348,507)		(350,951)
Embedded derivative	826		826		854
Carrying value of liability component	227,319		227,319		224,903
Equity component - net carrying value	230,214		230,214		230,214
Interest expense related to debentures [Abstract]
Contractual coupon interest	3,235	$ 3,235	6,470	6,470
Non-cash amortization of debt discount	1,233	1,139	2,444	2,259
Non-cash amortization of deferred financing costs	48	49	95	95
Non-cash change in value of derivative liability	(1)	(127)	(28)	(100)
Total interest expense related to the debentures	4,515	4,296	8,981	8,724
Convertible Senior Debentures, Due 2040 [Member]
Debt Instrument [Line Items]
Convertible Debt, Noncurrent	109,291		$ 109,291		108,120
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 conversion rate	76.6985
Debt effective conversion price | $ / shares	$ 13.04		$ 13.04
Debt Instrument, Convertible, Stock Price Trigger | $ / shares			$ 16.95
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	(166,058)		(166,058)		(167,273)
Embedded derivative	349		349		393
Carrying value of liability component	109,291		109,291		108,120
Equity component - net carrying value	110,094		110,094		110,094
Interest expense related to debentures [Abstract]
Contractual coupon interest	1,547	1,547	3,094	3,094
Non-cash amortization of debt discount	613	567	1,215	1,123
Non-cash amortization of deferred financing costs	22	22	44	44
Non-cash change in value of derivative liability	(19)	(41)	(44)	(35)
Total interest expense related to the debentures	2,163	2,095	4,309	4,226
Convertible Senior Debentures, Due 2041 [Member]
Debt Instrument [Line Items]
Convertible Debt, Noncurrent	56,072		$ 56,072		55,442
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 conversion rate	55.9705
Debt effective conversion price | $ / shares	$ 17.87		$ 17.87
Debt Instrument, Convertible, Stock Price Trigger | $ / shares			$ 23.23
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	(94,221)		(94,221)		(94,843)
Embedded derivative	293		293		285
Carrying value of liability component	56,072		56,072		55,442
Equity component - net carrying value	62,246		62,246		62,246
Interest expense related to debentures [Abstract]
Contractual coupon interest	844	844	1,688	1,688
Non-cash amortization of debt discount	314	289	622	573
Non-cash amortization of deferred financing costs	12	13	24	24
Non-cash change in value of derivative liability	6	(72)	8	(34)
Total interest expense related to the debentures	1,176	1,074	2,342	2,251
Convertible Senior Debentures, Due 2042 [Member]
Debt Instrument [Line Items]
Convertible Debt, Noncurrent	61,956		$ 61,956		61,341
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 conversion rate	90.1791
Debt effective conversion price | $ / shares	$ 11.09		$ 11.09
Debt Instrument, Convertible, Stock Price Trigger | $ / shares			$ 14.42
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	(88,228)		(88,228)		(88,835)
Embedded derivative	184		184		176
Carrying value of liability component	61,956		61,956		61,341
Equity component - net carrying value	57,874		57,874		$ 57,874
Interest expense related to debentures [Abstract]
Contractual coupon interest	844	844	1,688	1,688
Non-cash amortization of debt discount	306	283	607	563
Non-cash amortization of deferred financing costs	14	14	27	27
Non-cash change in value of derivative liability	12	(14)	8	(31)
Total interest expense related to the debentures	$ 1,176	$ 1,127	$ 2,330	$ 2,247