Long-Term Debt (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 30, 2019 USD ($) $ / shares	Jun. 30, 2018	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Debt Instruments [Abstract]
Credit facility	$ 0			$ 0
Deferred Financing Costs	(14,028)			(14,968)
Long-term debt	492,830			494,509
Less current portion	0			0
Long-term debt, less current portion	492,830			494,509
Interest expense [Abstract]
Contractual coupon interest	3,523		$ 3,235
Non-cash amortization of debt discount	3,490		1,309
Non-cash amortization of deferred financing costs	456		47
Non-cash change in value of derivative liability	(18)		161
Total interest expense related to the debentures	7,451		4,752
Purchase price of extinguished debt	22,695
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	(1,307)		0
Convertible Senior Debentures, Due 2040 [Member]
Debt Instruments [Abstract]
Convertible Debt, Noncurrent	$ 144			539
Issuance date	Nov. 09, 2010
Debt maturity date	Nov. 15, 2040
Cash coupon rate	2.25%
Nonconvertible debt borrowing rate at issuance	8.00%
Effective conversion rate	78.7076
Effective conversion price (in dollars per share) | $ / shares	$ 12.71
130% of the conversion price (in dollars per share) | $ / shares	$ 16.52
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%
Liability and equity components of convertible debentures [Abstract]
Principal amount of debt	$ 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, Noncurrent	$ 8,085			12,812
Issuance date	May 13, 2011
Debt maturity date	May 15, 2041
Cash coupon rate	2.25%
Nonconvertible debt borrowing rate at issuance	8.375%
Effective conversion rate	57.4367
Effective conversion price (in dollars per share) | $ / shares	$ 17.41
130% of the conversion price (in dollars per share) | $ / shares	$ 22.63
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%
Liability and equity components of convertible debentures [Abstract]
Principal amount of debt	$ 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, Noncurrent	0			923
Interest expense [Abstract]
Principal amount of repurchased debt	2,168
Net carrying value of repurchased debt	924
Convertible Senior Notes, Due 2025 [Member]
Debt Instruments [Abstract]
Convertible Debt, Noncurrent	$ 498,629			495,203
Issuance date	Jun. 12, 2018
Debt maturity date	Jun. 15, 2025	Jun. 15, 2025
Cash coupon rate	2.25%
Nonconvertible debt borrowing rate at issuance	5.50%
Effective conversion rate	31.7536
Effective conversion price (in dollars per share) | $ / shares	$ 31.49
130% of the conversion price (in dollars per share) | $ / shares	$ 40.94
Debt instrument percentage of conversion price	130.00%
Debt instrument percentage of sales price of common stock	98.00%
Maximum threshold of quarterly cash dividends per share of common stock for not adjusting conversion rate of convertible notes | $ / shares	$ 0.085
Liability and equity components of convertible debentures [Abstract]
Principal amount of debt	$ 600,000
Interest expense [Abstract]
Contractual coupon interest	3,375		0
Non-cash amortization of debt discount	3,426		0
Non-cash amortization of deferred financing costs	454		0
Non-cash change in value of derivative liability	0		0
Total interest expense related to the debentures	7,255		0
Convertible Senior Debentures [Member]
Interest expense [Abstract]
Contractual coupon interest	148		3,235
Non-cash amortization of debt discount	64		1,309
Non-cash amortization of deferred financing costs	2		47
Non-cash change in value of derivative liability	(18)		161
Total interest expense related to the debentures	196		$ 4,752
Convertible Debt [Member]
Liability and equity components of convertible debentures [Abstract]
Principal amount of debt	621,140			636,556
Unamortized discount	(114,306)			(127,149)
Embedded derivative	24			70
Carrying value of liability component	506,858			509,477
Equity component - net carrying value	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
Unamortized discount	(101,371)			(104,797)
Embedded derivative	0			0
Carrying value of liability component	498,629			495,203
Equity component - net carrying value	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			36,556
Unamortized discount	(12,935)			(22,352)
Embedded derivative	24			70
Carrying value of liability component	8,229			14,274
Equity component - net carrying value	$ 8,767			$ 15,092