CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands		Total	Common Stock	Additional Paid-In Capital	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Retained Earnings (Accumulated Deficit)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment upon adoption of ASU 2016-09		$ 169		$ (1,163)			$ 1,332
Balance at Dec. 31, 2015		699,613	$ 0	774,022	$ 0	$ (13,519)	(60,890)
Balance (in shares) at Dec. 31, 2015			75,982,802
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercises of employee stock options		20,599	$ 0	20,599
Issuance of common stock upon exercises of employee stock options (in shares)			1,290,836
Issuance of common stock upon vesting of RSUs		0	$ 0
Issuance of common stock upon vesting of RSUs (in shares)			1,814,138
Issuance of common stock for employee stock purchase plan		8,923	$ 0	8,923
Issuance of common stock for employee stock purchase plan (in shares)			342,057
Stock-based compensation (inclusive of capitalized stock-based compensation)		90,602		90,602
Foreign currency translation adjustments		(2,057)				(2,057)
Net income (loss)		(1,711)					(1,711)
Balance at Dec. 31, 2016		816,138	$ 0	892,983	0	(15,576)	(61,269)
Balance (in shares) at Dec. 31, 2016			79,429,833.000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercises of employee stock options		29,997	$ 0	29,997
Issuance of common stock upon exercises of employee stock options (in shares)			1,519,771
Issuance of common stock upon vesting of RSUs		0	$ 0
Issuance of common stock upon vesting of RSUs (in shares)			2,702,838
Issuance of common stock for employee stock purchase plan		10,920	$ 0	10,920
Issuance of common stock for employee stock purchase plan (in shares)			373,580
Stock-based compensation (inclusive of capitalized stock-based compensation)		106,639		106,639
Shares withheld related to net share settlement of equity awards		(2,522)		(2,522)
Repurchase of common stock	[1]	(12,602)	$ 0		(46)		(12,556)
Repurchase of common stock (in shares)	[1]		(301,106)
Foreign currency translation adjustments		7,132				7,132
Net income (loss)		152,995					152,995
Balance at Dec. 31, 2017		$ 1,108,697	$ 0	1,038,017	(46)	(8,444)	79,170
Balance (in shares) at Dec. 31, 2017		83,724,916	83,724,916
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercises of employee stock options		$ 15,581		15,581
Issuance of common stock upon exercises of employee stock options (in shares)		779,871	779,871
Issuance of common stock upon vesting of RSUs		$ 0	$ 0
Issuance of common stock upon vesting of RSUs (in shares)			1,946,476
Issuance of common stock for employee stock purchase plan		14,198	$ 0	14,198
Issuance of common stock for employee stock purchase plan (in shares)			442,679
Stock-based compensation (inclusive of capitalized stock-based compensation)		121,878		121,878
Shares withheld related to net share settlement of equity awards		(50,212)		(50,212)
Repurchase of common stock	[1]	(187,397)	$ 0		46		(187,443)
Repurchase of common stock (in shares)	[1]		(4,897,103)
Foreign currency translation adjustments		(2,577)				(2,577)
Net income (loss)		55,350					55,350
Balance at Dec. 31, 2018		$ 1,075,518	$ 0	$ 1,139,462	$ 0	$ (11,021)	$ (52,923)
Balance (in shares) at Dec. 31, 2018		81,996,839	81,996,839

[1] 1,100 shares were excluded from the share total as of December 31, 2017 that had been repurchased but not yet retired, and were held as treasury stock as of that date. Those shares were retired during the year ended December 31, 2018.