Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment for ASU adoption | Accounting Standards Update 2016-01	$ 0			$ 7,234	$ (7,234)
Cumulative effect adjustment for ASU adoption | Accounting Standards Update 2016-16	(746)			(746)
Beginning balance (in shares) at Dec. 31, 2017		174,275,864
Beginning balance at Dec. 31, 2017	$ 778,744	$ 174	$ 1,731,367	(958,564)	5,767
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued under employee stock plans (in shares)	2,287,099	2,287,099
Common stock issued under employee stock plans	$ 52,661	$ 3	52,658
Taxes paid related to net share settlement of equity awards	(85,617)		(85,617)
Stock-based compensation	121,709		121,709
Stock Issued During Period, Value, Conversion of Convertible Securities	(45,217)		(45,217)
Benefit from exercise of 2018 Note Hedges	44,510		44,510
Other comprehensive income (loss), net	(11,503)				(11,503)
Net income (loss)	10,622			10,622
Beginning balance (in shares) at Mar. 31, 2018		176,562,963
Beginning balance at Mar. 31, 2018	865,163	$ 177	1,819,410	(941,454)	(12,970)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment for ASU adoption | Accounting Standards Update 2016-02	(162)			(162)
Beginning balance (in shares) at Dec. 31, 2018		180,175,355
Beginning balance at Dec. 31, 2018	$ 1,111,199	$ 180	2,093,834	(978,780)	(4,035)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issued under employee stock plans (in shares)	1,882,821	1,882,821
Common stock issued under employee stock plans	$ 53,102	$ 2	53,100
Taxes paid related to net share settlement of equity awards	(139,470)		(139,470)
Stock-based compensation	157,469		157,469
Settlement of 2018 Warrants (in shares)		2,680,993
Settlement of 2018 Warrants and 2018 Notes conversion feature	0	$ 3	(3)
Other comprehensive income (loss), net	14,358				14,358
Net income (loss)	(1,545)			(1,545)
Beginning balance (in shares) at Mar. 31, 2019		184,739,169
Beginning balance at Mar. 31, 2019	$ 1,194,951	$ 185	$ 2,164,930	$ (980,487)	$ 10,323