Consolidated Statements of Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2018	$ 834,525	$ 61	$ 1,397,829	$ (8,628)	$ 17,241	$ (571,978)
Beginning Balance, Shares at Dec. 31, 2018		56,648				(5,116)
Issuance of common stock under employee and director equity option and purchase plans	(8,177)	$ 0	202	0	0	$ (8,379)
Issuance of common stock under employee and director equity option and purchase plans, Shares		399				(146)
Stock-based compensation expense	4,766	$ 0	4,766	0	0	$ 0
Issuance of common stock in connection with royalty milestone achievement	0	$ 0	0	0	0	0
Issuance of common stock in connection with royalty milestone achievement, Shares		72
Consolidated net income (loss)	9,386	$ 0	0	0	9,386	0
Other comprehensive (loss) income	(494)	0	0	(494)	0	0
Ending Balance at Mar. 31, 2019	840,006	$ 61	1,402,797	(9,122)	26,627	$ (580,357)
Ending Balance, Shares at Mar. 31, 2019		57,119				(5,262)
Beginning Balance at Dec. 31, 2018	834,525	$ 61	1,397,829	(8,628)	17,241	$ (571,978)
Beginning Balance, Shares at Dec. 31, 2018		56,648				(5,116)
Consolidated net income (loss)	24,348
Other comprehensive (loss) income	76
Ending Balance at Jun. 30, 2019	862,724	$ 62	1,413,934	(8,552)	41,589	$ (584,309)
Ending Balance, Shares at Jun. 30, 2019		57,357				(5,328)
Beginning Balance at Mar. 31, 2019	840,006	$ 61	1,402,797	(9,122)	26,627	$ (580,357)
Beginning Balance, Shares at Mar. 31, 2019		57,119				(5,262)
Issuance of common stock under employee and director equity option and purchase plans	364	$ 1	4,315	0	0	$ (3,952)
Issuance of common stock under employee and director equity option and purchase plans, Shares		238				(66)
Stock-based compensation expense	6,822	$ 0	6,822	0	0	$ 0
Consolidated net income (loss)	14,962	0	0	0	14,962	0
Other comprehensive (loss) income	570	0	0	570	0	0
Ending Balance at Jun. 30, 2019	862,724	$ 62	1,413,934	(8,552)	41,589	$ (584,309)
Ending Balance, Shares at Jun. 30, 2019		57,357				(5,328)
Beginning Balance at Dec. 31, 2019	915,207	$ 62	1,429,854	(9,418)	82,475	$ (587,766)
Beginning Balance, Shares at Dec. 31, 2019		57,525				(5,380)
Issuance of common stock under employee and director equity option and purchase plans	(3,818)	$ 0	119	0	0	$ (3,937)
Issuance of common stock under employee and director equity option and purchase plans, Shares		167				(59)
Stock-based compensation expense	2,786	$ 0	2,786	0	0	$ 0
Tax benefits related to convertible note issuance	484	0	484	0	0	0
Shares repurchased	(75,000)	$ 0	0	0	0	$ (75,000)
Shares repurchased ,Shares		0				(1,085)
Sale of warrants	47,070	$ 0	47,070	0	0	$ 0
Convertible note hedge	(78,300)	0	(78,300)	0	0	0
Equity component of convertible note issuance	78,268	0	78,268	0	0	0
Debt issuance costs attributable to convertible feature	(1,987)	0	(1,987)	0	0	0
Consolidated net income (loss)	5,298	0	0	0	5,298	0
Other comprehensive (loss) income	(3,809)	0	0	(3,809)	0	0
Ending Balance at Mar. 31, 2020	886,199	$ 62	1,478,294	(13,227)	87,773	$ (666,703)
Ending Balance, Shares at Mar. 31, 2020		57,692				(6,524)
Beginning Balance at Dec. 31, 2019	915,207	$ 62	1,429,854	(9,418)	82,475	$ (587,766)
Beginning Balance, Shares at Dec. 31, 2019		57,525				(5,380)
Consolidated net income (loss)	(44,717)
Other comprehensive (loss) income	(2,757)
Ending Balance at Jun. 30, 2020	894,890	$ 62	1,536,156	(12,175)	37,758	$ (666,911)
Ending Balance, Shares at Jun. 30, 2020		57,779				(6,528)
Beginning Balance at Mar. 31, 2020	886,199	$ 62	1,478,294	(13,227)	87,773	$ (666,703)
Beginning Balance, Shares at Mar. 31, 2020		57,692				(6,524)
Issuance of common stock under employee and director equity option and purchase plans	3,663	$ 0	3,871	0	0	$ (208)
Issuance of common stock under employee and director equity option and purchase plans, Shares		87				(4)
Stock-based compensation expense	7,081	$ 0	7,081	0	0	$ 0
Sale of warrants	46,845	0	46,845	0	0	0
Debt issuance costs attributable to convertible feature	65	0	65	0	0	0
Consolidated net income (loss)	(50,015)	0	0	0	(50,015)	0
Other comprehensive (loss) income	1,052	0	0	1,052	0	0
Ending Balance at Jun. 30, 2020	$ 894,890	$ 62	$ 1,536,156	$ (12,175)	$ 37,758	$ (666,911)
Ending Balance, Shares at Jun. 30, 2020		57,779				(6,528)