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)	(51,046)			(51,046)
Foreign currency translation adjustment	(1,771)				(1,771)
Unrealized gain (loss) on marketable securities, net of tax	(692)				(692)
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		1,367
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	693	$ 1	692
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	9,402		9,402
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income	626,288
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income | Equity Securities [Member]	1,058			1,058
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income | Accounting Standards Update 2014-09 [Member]				626,288
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)
Balance (in shares) at Mar. 31, 2018		107,485
Balance at Mar. 31, 2018	1,118,998	$ 107	1,196,158	(74,255)	(3,012)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	(15,357)			(15,357)
Foreign currency translation adjustment	(4,660)				(4,660)
Unrealized gain (loss) on marketable securities, net of tax	112				112
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		528
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	4,535	$ 1	4,534
Stock Repurchased and Retired During Period, Shares		668
Stock Repurchased and Retired During Period, Value	31	$ 1	(7,741)	7,771	0
Stock-based compensation	1,888		1,888
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)
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)	(63,556)			(63,556)
Foreign currency translation adjustment	(174)				(174)
Unrealized gain (loss) on marketable securities, net of tax	84				84
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		2,109
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	6,022	$ 2	6,020
Stock-based compensation	14,269		14,269
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income | Accounting Standards Update 2016-02 [Member]	4,469			4,469
Balance (in shares) at Jun. 30, 2019		111,127
Balance at Jun. 30, 2019	973,226	$ 111	1,246,877	(263,381)	(10,381)
Balance (in shares) at Mar. 31, 2019		110,396
Balance at Mar. 31, 2019	999,887	$ 110	1,234,846	(226,401)	(8,668)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	(36,980)			(36,980)
Foreign currency translation adjustment	(1,749)				(1,749)
Unrealized gain (loss) on marketable securities, net of tax	36				36
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		731
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	4,952	$ 1	4,951
Stock-based compensation	7,080		7,080
Balance (in shares) at Jun. 30, 2019		111,127
Balance at Jun. 30, 2019	$ 973,226	$ 111	$ 1,246,877	$ (263,381)	$ (10,381)