Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	APIC	Notes Receivable from Related Parties	Accumulated deficit
Beginning balance (in shares) at Dec. 31, 2013		59,955,343
Beginning balance at Dec. 31, 2013	$ 112,180	$ 6	$ 275,803	$ (1,069)	$ (162,560)
Increase (Decrease) in Stockholders' Equity
Net loss	(48,429)				(48,429)
Issuance of common stock in connection with initial public offering, net of underwriting discounts and offering costs (in shares)		8,941,250
Issuance of common stock in connection with initial public offering, net of underwriting discounts and offering costs	69,151	$ 1	69,150
Conversion of Series A convertible preferred stock in connection with initial public offering (in shares)		2,857,143
Conversion of Series A convertible preferred stock in connection with initial public offering	29,224		29,224
Issuance of common stock in follow-on offering, net of underwriting discounts and offering costs (in shares)		1,960,390
Issuance of common stock in follow-on offering, net of underwriting discounts and offering costs	30,762		30,762
Stock-based compensation	30,582		30,582
Issuance of warrants relating to marketing agreements	9,861		9,861
Net exercise of warrants to purchase common stock (in shares)		3,357,867
Net exercise of warrants to purchase common stock	9,461	$ 1	9,460
Shares issued in connection with employee stock plans, net of shares withheld for employee taxes (in shares)		2,739,776
Shares issued in connection with employee stock plans, net of shares withheld for employee taxes	5,313		5,313
Recovery of short swing profits	14		14
Imputed interest on notes receivable	10		10
Interest income on notes receivable	(3)			(3)
Repayment of notes receivable	1,072			1,072
Ending balance at Dec. 31, 2014	249,198	$ 8	460,179	0	(210,989)
Ending balance (in shares) at Dec. 31, 2014		79,811,769
Increase (Decrease) in Stockholders' Equity
Net loss	(64,911)				(64,911)
Stock-based compensation	43,888		43,888
Repurchase of common stock awards	(100)		(100)
Issuance of warrants relating to marketing agreements	(803)		(803)
Net exercise of warrants to purchase common stock (in shares)		959,676
Shares issued in connection with employee stock plans, net of shares withheld for employee taxes (in shares)		2,245,290
Shares issued in connection with employee stock plans, net of shares withheld for employee taxes	5,420		5,420
Ending balance at Dec. 31, 2015	$ 232,692	$ 8	508,584	0	(275,900)
Ending balance (in shares) at Dec. 31, 2015	83,016,735	83,016,735
Increase (Decrease) in Stockholders' Equity
Cumulative-effect of accounting change adopted as of January 1, 2016			627		(627)
Net loss	$ (41,708)				(41,708)
Stock-based compensation	25,751		25,751
Issuance of warrants relating to marketing agreements	46		46
Shares issued in connection with employee stock plans, net of shares withheld for employee taxes (in shares)		3,142,792
Shares issued in connection with employee stock plans, net of shares withheld for employee taxes	7,800	$ 1	7,799
Ending balance at Dec. 31, 2016	$ 224,581	$ 9	$ 542,807	$ 0	$ (318,235)
Ending balance (in shares) at Dec. 31, 2016	86,159,527	86,159,527