Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss, Net [Member]	Retained Deficit [Member]	Total
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2017	$ 153	$ 2,713,161	$ (67,427)	$ (1,513,458)	$ 1,132,429
Beginning balance, shares at Dec. 31, 2017					153,263,097
Net loss				(59,724)	$ (59,724)
Foreign currency translation adjustment			4,388		4,388
Stock-based compensation expense, net of forfeitures		6,229			6,229
Transactions under stock plans, value	1	(5,154)			$ (5,153)
Transactions under stock plans, shares					974,165
Stockholders' Equity Attributable to Parent, Ending Balance at Mar. 31, 2018	154	2,714,236	(63,039)	(1,573,182)	$ 1,078,169
Ending balance, shares at Mar. 31, 2018					154,237,262
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2017	153	2,713,161	(67,427)	(1,513,458)	$ 1,132,429
Beginning balance, shares at Dec. 31, 2017					153,263,097
Net loss					$ (107,930)
Foreign currency translation adjustment					(3,491)
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2018	155	2,728,167	(70,918)	(1,621,388)	$ 1,036,016
Ending balance, shares at Sep. 30, 2018					154,530,114
Stockholders' Equity Attributable to Parent, Beginning Balance at Mar. 31, 2018	154	2,714,236	(63,039)	(1,573,182)	$ 1,078,169
Beginning balance, shares at Mar. 31, 2018					154,237,262
Net loss				(26,390)	$ (26,390)
Foreign currency translation adjustment			(7,053)		(7,053)
Stock-based compensation expense, net of forfeitures		6,113			6,113
Transactions under stock plans, value		(30)			$ (30)
Transactions under stock plans, shares					90,535
Shares issued under Employee Stock Purchase Plan, value	1	1,905			$ 1,906
Shares issued under Employee Stock Purchase Plan					197,830
Stockholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2018	155	2,722,224	(70,092)	(1,599,572)	$ 1,052,715
Ending balance, shares at Jun. 30, 2018					154,525,627
Net loss				(21,816)	$ (21,816)
Foreign currency translation adjustment			(826)		(826)
Stock-based compensation expense, net of forfeitures		5,948			5,948
Transactions under stock plans, value		(5)			$ (5)
Transactions under stock plans, shares					4,487
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2018	155	2,728,167	(70,918)	(1,621,388)	$ 1,036,016
Ending balance, shares at Sep. 30, 2018					154,530,114
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2018	$ 155	2,735,125	(73,177)	(2,371,364)	$ 290,739
Beginning balance, shares at Dec. 31, 2018	154,885,418
Net loss				(47,705)	(47,705)
Foreign currency translation adjustment			1,073		1,073
Stock-based compensation expense, net of forfeitures		5,625			5,625
Transactions under stock plans, value	$ 1	(1,667)			(1,666)
Transactions under stock plans, shares	1,071,182
Stockholders' Equity Attributable to Parent, Ending Balance at Mar. 31, 2019	$ 156	2,739,083	(72,104)	(2,419,069)	248,066
Ending balance, shares at Mar. 31, 2019	155,956,600
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 31, 2018	$ 155	2,735,125	(73,177)	(2,371,364)	290,739
Beginning balance, shares at Dec. 31, 2018	154,885,418
Net loss					(157,196)
Foreign currency translation adjustment					(3,810)
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2019	$ 157	2,748,477	(76,987)	(2,528,560)	143,087
Ending balance, shares at Sep. 30, 2019	156,573,565
Stockholders' Equity Attributable to Parent, Beginning Balance at Mar. 31, 2019	$ 156	2,739,083	(72,104)	(2,419,069)	248,066
Beginning balance, shares at Mar. 31, 2019	155,956,600
Net loss				(71,050)	(71,050)
Foreign currency translation adjustment			(1,916)		(1,916)
Stock-based compensation expense, net of forfeitures		4,650			4,650
Transactions under stock plans, value		(10)			(10)
Transactions under stock plans, shares	116,374
Shares issued under Employee Stock Purchase Plan, value	$ 1	650			651
Shares issued under Employee Stock Purchase Plan	500,186
Stockholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2019	$ 157	2,744,373	(74,020)	(2,490,119)	180,391
Ending balance, shares at Jun. 30, 2019	156,573,160
Net loss				(38,441)	(38,441)
Foreign currency translation adjustment			(2,967)		(2,967)
Stock-based compensation expense, net of forfeitures		4,104			4,104
Transactions under stock plans, shares	405
Stockholders' Equity Attributable to Parent, Ending Balance at Sep. 30, 2019	$ 157	$ 2,748,477	$ (76,987)	$ (2,528,560)	$ 143,087
Ending balance, shares at Sep. 30, 2019	156,573,565