Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance (in shares) at Dec. 31, 2015	39,389,290
Balance at Dec. 31, 2015	$ 39	$ 392,616	$ (102,741)	$ 756	$ 290,670
Issuance of common stock from exercise of stock options (in shares)	587,229
Issuance of common stock from exercise of stock options	$ 1	5,786			5,787
Issuance of common stock from restricted stock unit grants, net of shares withheld for tax (in shares)	1,041,743
Issuance of common stock from restricted stock unit grants, net of shares withheld for tax	$ 1	(20,478)			$ (20,477)
Issuance of common stock from employee stock purchase plan (in shares)	285,101				285,101
Issuance of common stock from employee stock purchase plan		5,518			$ 5,518
Stock-based compensation expense		30,192			30,192
Conversion feature of convertible debt, net of issuance costs		68,834			68,834
Purchase of capped calls		(22,540)			(22,540)
Net income (loss)			99,456		99,456
Cumulative effect of change in accounting principle			5,261		5,261
Other comprehensive loss, net				(177)	(177)
Balance (in shares) at Dec. 31, 2016	41,303,363
Balance at Dec. 31, 2016	$ 41	459,928	1,976	579	462,524
Issuance of common stock from exercise of stock options (in shares)	300,982
Issuance of common stock from exercise of stock options	$ 1	2,174			2,175
Issuance of common stock from restricted stock unit grants, net of shares withheld for tax (in shares)	1,004,785
Issuance of common stock from restricted stock unit grants, net of shares withheld for tax	$ 1	(27,776)			$ (27,775)
Issuance of common stock from employee stock purchase plan (in shares)	171,099				171,099
Issuance of common stock from employee stock purchase plan		5,776			$ 5,776
Stock-based compensation expense		44,832			44,832
Net income (loss)			(74,904)		(74,904)
Cumulative effect of change in accounting principle			(1,217)		(1,217)
Other comprehensive loss, net				(10)	(10)
Balance (in shares) at Dec. 31, 2017	42,780,229
Balance at Dec. 31, 2017	$ 43	484,934	(74,145)	569	$ 411,401
Issuance of common stock from exercise of stock options (in shares)	187,742				187,742
Issuance of common stock from exercise of stock options		719			$ 719
Issuance of common stock from restricted stock unit grants, net of shares withheld for tax (in shares)	1,041,258
Issuance of common stock from restricted stock unit grants, net of shares withheld for tax	$ 1	(19,286)			$ (19,285)
Issuance of common stock from employee stock purchase plan (in shares)	283,493				283,493
Issuance of common stock from employee stock purchase plan		5,906			$ 5,906
Stock-based compensation expense		63,884			63,884
Net income (loss)			(95,751)		(95,751)
Other comprehensive loss, net				(180)	(180)
Balance (in shares) at Dec. 31, 2018	44,292,722
Balance at Dec. 31, 2018	$ 44	$ 536,157	$ (169,896)	$ 389	$ 366,694