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)	(35,689)	0	0	(35,689)	0
Foreign currency translation adjustment	2,889				2,889
Unrealized gain (loss) on marketable securities, net of tax	(804)	0	0	0	(804)
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	(3,842)	$ 0	(3,842)	0	0
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		839
Stock Repurchased and Retired During Period, Shares		(3,118)
Stock Repurchased and Retired During Period, Value		$ (3)	(20,312)	(29,685)	0
Repurchase and retirement of common stock under repurchase plan, including prepayment under accelerated share repurchase program	(50,000)
Stock-based compensation	7,514	$ 0	7,514	0	0
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			626,288
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)
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)	(26,576)	0	0	(26,576)	0
Foreign currency translation adjustment	1,575				1,575
Unrealized gain (loss) on marketable securities, net of tax	48	0	0	0	48
Issuance of common stock upon exercise of options, equity stock and employee stock purchase plan	1,070	$ 1	1,069	0	0
Issuance of common stock upon exercise of options, equity stock and stock units, and employee stock purchase plan (in shares)		1,378
Stock-based compensation	7,189	$ 0	7,189	0	0
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 Mar. 31, 2019		110,396
Balance at Mar. 31, 2019	$ 999,887	$ 110	$ 1,234,846	$ (226,401)	$ (8,668)