Long-Term Debt (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 29, 2019	Mar. 30, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018	Dec. 31, 2018
Line of Credit Facility [Line Items]
Line of credit facility, decrease in commitment fee				0.05%
Debt Instruments [Abstract]
Credit facility	$ 28,000			$ 28,000		$ 0
Deferred financing costs	(18,486)			(18,486)		(14,968)
Long-term debt	519,863			519,863		494,509
Less current portion	0			0		0
Long-term debt, less current portion	519,863			519,863		494,509
Interest expense [Abstract]
Contractual coupon interest	3,494		$ 3,405	7,017	$ 6,640
Non-cash amortization of debt discount	3,495		1,655	6,985	2,964
Non-cash amortization of deferred financing costs	456		190	912	237
Non-cash change in value of derivative liability	(4)		(156)	(22)	5
Total interest expense related to the debentures	7,441		5,094	14,892	9,846
Allocated liability component of repurchased debt		$ 7,311
Allocated equity component of repurchased debt		15,384
Loss on extinguishment of debt, including the write-off of portion of unamortized debt issuance costs	0	(1,307)	$ (17,309)	(1,307)	(17,309)
Convertible Senior Notes, Due 2025 [Member]
Debt Instruments [Abstract]
Convertible debt	$ 502,071			$ 502,071		495,203
Issuance date				Jun. 12, 2018
Debt maturity date				Jun. 15, 2025
Cash coupon rate	2.25%			2.25%
Nonconvertible debt borrowing rate at issuance	5.50%			5.50%
Effective conversion rate				31.7738
Effective conversion price (in dollars per share)	$ 31.47			$ 31.47
130% of the conversion price (in dollars per share)			$ 40.94	$ 40.91
Debt instrument percentage of conversion price				130.00%
Debt instrument percentage of sales price of common stock	98.00%			98.00%
Maximum threshold of quarterly cash dividends per share of common stock for not adjusting conversion rate of convertible notes				$ 0.085
Liability and equity components of convertible debentures [Abstract]
Principal amount of debt	$ 600,000			$ 600,000
Interest expense [Abstract]
Contractual coupon interest	3,375		$ 713	6,750	713
Non-cash amortization of debt discount	3,442		556	6,868	556
Non-cash amortization of deferred financing costs	454		151	908	151
Non-cash change in value of derivative liability	0		0	0	0
Total interest expense related to the debentures	7,271		1,420	14,526	1,420
Convertible Senior Debentures, Due 2040 [Member]
Debt Instruments [Abstract]
Convertible debt	$ 146			$ 146		539
Issuance date				Nov. 09, 2010
Debt maturity date				Nov. 15, 2040
Cash coupon rate	2.25%			2.25%
Nonconvertible debt borrowing rate at issuance	8.00%			8.00%
Effective conversion rate				79.1822
Effective conversion price (in dollars per share)	$ 12.63			$ 12.63
130% of the conversion price (in dollars per share)				$ 16.42
Convertible senior debentures call date				Nov. 20, 2020
Conversion period before maturity date				3 months
Debt instrument percentage of conversion price				130.00%
Debt instrument percentage of sales price of common stock	98.00%			98.00%
Liability and equity components of convertible debentures [Abstract]
Principal amount of debt	$ 350			$ 350
Interest expense [Abstract]
Principal amount of repurchased debt		960
Net carrying value of repurchased debt		396
Convertible Senior Debentures, Due 2041 [Member]
Debt Instruments [Abstract]
Convertible debt	$ 8,132			$ 8,132		12,812
Issuance date				May 13, 2011
Debt maturity date				May 15, 2041
Cash coupon rate	2.25%			2.25%
Nonconvertible debt borrowing rate at issuance	8.375%			8.375%
Effective conversion rate				57.7830
Effective conversion price (in dollars per share)	$ 17.31			$ 17.31
130% of the conversion price (in dollars per share)				$ 22.50
Convertible senior debentures call date				May 20, 2021
Conversion period before maturity date				3 months
Debt instrument percentage of conversion price				130.00%
Debt instrument percentage of sales price of common stock	98.00%			98.00%
Liability and equity components of convertible debentures [Abstract]
Principal amount of debt	$ 20,790			$ 20,790
Interest expense [Abstract]
Principal amount of repurchased debt		12,288
Net carrying value of repurchased debt		4,770
Convertible Senior Debentures, Due 2042 [Member]
Debt Instruments [Abstract]
Convertible debt	0			0		923
Interest expense [Abstract]
Principal amount of repurchased debt		2,168
Net carrying value of repurchased debt		924
Convertible Senior Debentures [Member]
Interest expense [Abstract]
Contractual coupon interest	119		2,692	267	5,927
Non-cash amortization of debt discount	53		1,099	117	2,408
Non-cash amortization of deferred financing costs	2		39	4	86
Non-cash change in value of derivative liability	(4)		(156)	(22)	5
Total interest expense related to the debentures	$ 170		$ 3,674	$ 366	$ 8,426
Purchase price of extinguished debt		$ 22,695
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate				1.50%
Commitment fees				0.25%
Incremental revolving commitments				$ 300,000
Line of credit facility, commitment fee percentage				0.25%
Line of credit facility, expiration date				Jun. 05, 2024
Line of credit facility, initiation date	Jun. 05, 2019
Line of credit facility, maximum borrowing capacity	$ 750,000			$ 750,000
Restricted payments (annual limit)	100,000			100,000
Restricted payments (total limit)	300,000			300,000
Restricted payments (rollover limit)	25,000			$ 25,000
Restricted payments pro form ratio				2.50
Investments pro forma ratio				2.75
Event of default - judgment limit	50,000			$ 50,000
Previous Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit facility, expiration date				Dec. 10, 2020
Line of credit facility, maximum borrowing capacity	640,000			$ 640,000
Convertible Debt [Member]
Liability and equity components of convertible debentures [Abstract]
Principal amount of debt	621,140			621,140		636,556
Unamortized discount	(110,811)			(110,811)		(127,149)
Embedded derivative	20			20		70
Carrying value of liability component	510,349			510,349		509,477
Equity component - net carrying value	94,029			94,029		100,354
Convertible Debt [Member] | Convertible Senior Notes, Due 2025 [Member]
Liability and equity components of convertible debentures [Abstract]
Principal amount of debt	600,000			600,000		600,000
Unamortized discount	(97,929)			(97,929)		(104,797)
Embedded derivative	0			0		0
Carrying value of liability component	502,071			502,071		495,203
Equity component - net carrying value	85,262			85,262		85,262
Convertible Debt [Member] | Convertible Senior Debentures [Member]
Liability and equity components of convertible debentures [Abstract]
Principal amount of debt	21,140			21,140		36,556
Unamortized discount	(12,882)			(12,882)		(22,352)
Embedded derivative	20			20		70
Carrying value of liability component	8,278			8,278		14,274
Equity component - net carrying value	$ 8,767			$ 8,767		$ 15,092