Organization and Basis of Presentation (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	Jul. 07, 2015	Mar. 31, 2016	Dec. 31, 2015	Jul. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Accumulated deficit		$ (340,376)	$ (325,342)
Cash, cash equivalents, and short-term investments		103,500
Cash and cash equivalents		76,583	117,185		$ 22,939	$ 37,900
Restricted cash		$ 600	$ 600
Issuance of common stock - IPO	10,350,000
Common stock shares authorized	200,000,000	200,000,000	200,000,000
Preferred stock shares authorized	5,000,000	5,000,000	5,000,000
Common stock warrants
Class of Stock [Line Items]
Common stock warrants issued in replacement of preferred stock warrants (in shares)		564,188
Preferred stock warrants
Class of Stock [Line Items]
Expiration of warrants to purchase capital stock (in shares)	482,964
Series C convertible preferred stock | Preferred stock warrants
Class of Stock [Line Items]
Preferred stock warrants replaced by common stock warrants (in shares)	285,714
Exercise price of preferred stock warrants replaced by common stock warrants (in dollars per share)	$ 3.50
Series D convertible preferred stock | Preferred stock warrants
Class of Stock [Line Items]
Preferred stock warrants replaced by common stock warrants (in shares)	160,000
Exercise price of preferred stock warrants replaced by common stock warrants (in dollars per share)	$ 6.00
Expiration of warrants to purchase capital stock (in shares)	64,217
Series E-1 convertible preferred stock | Preferred stock warrants
Class of Stock [Line Items]
Expiration of warrants to purchase capital stock (in shares)	215,807
Series E-2 convertible preferred stock | Preferred stock warrants
Class of Stock [Line Items]
Expiration of warrants to purchase capital stock (in shares)	202,940
Common Stock
Class of Stock [Line Items]
Shares issued for conversion of preferred stock	25,527,505
Common stock issued upon exercise or exchange of warrants (in shares)	380,902
Common Stock | Common stock warrants
Class of Stock [Line Items]
Common stock issued upon exercise or exchange of warrants (in shares)	4,166
Common Stock | Preferred stock warrants, Series C
Class of Stock [Line Items]
Common stock warrants issued in replacement of preferred stock warrants (in shares)	142,857
Exercise price of common stock warrants issued in replacement of preferred stock warrants (in dollars per share)	$ 7.00
Common Stock | Preferred stock warrants, Series D
Class of Stock [Line Items]
Common stock issued upon exercise or exchange of warrants (in shares)	252,429
Common stock warrants issued in replacement of preferred stock warrants (in shares)	80,000
Exercise price of common stock warrants issued in replacement of preferred stock warrants (in dollars per share)	$ 12.00
Common Stock | Preferred stock warrants, Series E-1
Class of Stock [Line Items]
Common stock issued upon exercise or exchange of warrants (in shares)	300,059
Common Stock | Preferred stock warrants, Series E-2
Class of Stock [Line Items]
Common stock issued upon exercise or exchange of warrants (in shares)	200,996
IPO
Class of Stock [Line Items]
Aggregate offering proceeds	$ 155,000
Aggregate offering proceeds, net	$ 140,000
IPO | Common Stock
Class of Stock [Line Items]
Issuance of common stock - IPO	10,350,000
Public offering share price (in dollars per share)	$ 15.00
Over-allotment option | Common Stock
Class of Stock [Line Items]
Issuance of common stock - IPO	1,350,000
Asia | Letter agreement | Investor
Class of Stock [Line Items]
Proceeds reclassified from restricted cash to cash and cash equivalents				$ 3,500