CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated deficit	Accumulated other comprehensive gain (loss)
Balance (in shares) at Dec. 31, 2017		109,764
Balance at Dec. 31, 2017	$ 571,584	$ 110	$ 1,212,798	$ (636,227)	$ (5,097)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	(155,939)			(155,939)
Foreign currency translation adjustment	(2,798)				(2,798)
Unrealized gain (loss) on marketable securities, net of tax	(734)				(734)
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		2,099
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	3,295	$ 3	3,292
Stock repurchased and retired during period, shares		3,786
Stock repurchased and retired during period, value	50,031	$ 4	12,571	37,456	0
Stock-based compensation	15,591		15,591
Issuance of common stock in connection with maturity of convertible note, shares issued		424
Cumulative effect adjustment from adoption of new accounting pronouncement | Cumulative effect adjustment from adoption of ASU 2016-01	1,058			1,058
Cumulative effect adjustment from adoption of new accounting pronouncement | Cumulative effect adjustment from adoption of ASC 606	626,288			626,288
Balance (in shares) at Sep. 30, 2018		108,501
Balance at Sep. 30, 2018	1,008,314	$ 109	1,219,110	(202,276)	(8,629)
Balance (in shares) at Jun. 30, 2018		107,345
Balance at Jun. 30, 2018	1,105,485	$ 107	1,210,321	(97,383)	(7,560)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	(104,893)			(104,893)
Foreign currency translation adjustment	(1,027)				(1,027)
Unrealized gain (loss) on marketable securities, net of tax	(42)				(42)
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		732
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	2,602	$ 2	2,600
Stock-based compensation	6,189		6,189
Issuance of common stock in connection with maturity of convertible note, shares issued		424
Balance (in shares) at Sep. 30, 2018		108,501
Balance at Sep. 30, 2018	1,008,314	$ 109	1,219,110	(202,276)	(8,629)
Balance (in shares) at Dec. 31, 2018		109,018
Balance at Dec. 31, 2018	1,012,112	$ 109	1,226,588	(204,294)	(10,291)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	(80,887)			(80,887)
Foreign currency translation adjustment	(2,270)				(2,270)
Unrealized gain (loss) on marketable securities, net of tax	101				101
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		2,475
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	6,101	$ 2	6,099
Stock-based compensation	21,657		21,657
Cumulative effect adjustment from adoption of new accounting pronouncement | Cumulative effect adjustment from adoption of ASC 842	4,469			4,469
Balance (in shares) at Sep. 30, 2019		111,493
Balance at Sep. 30, 2019	961,283	$ 111	1,254,344	(280,712)	(12,460)
Balance (in shares) at Jun. 30, 2019		111,127
Balance at Jun. 30, 2019	973,226	$ 111	1,246,877	(263,381)	(10,381)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	(17,331)			(17,331)
Foreign currency translation adjustment	(2,096)				(2,096)
Unrealized gain (loss) on marketable securities, net of tax	17				17
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		366
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	79	$ 0	79
Stock-based compensation	7,388		7,388
Balance (in shares) at Sep. 30, 2019		111,493
Balance at Sep. 30, 2019	$ 961,283	$ 111	$ 1,254,344	$ (280,712)	$ (12,460)