Condensed Consolidated Statements of Changes in Convertible Preferred Stock and Stockholder's Equity (Deficit) (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in-Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2014	$ 144,941	$ 21	$ 238,402	$ (5)	$ (93,477)
Balance (in shares) at Dec. 31, 2014		21,440
Exercise of stock options	593	$ 1	592
Exercise of stock options (in shares)		109
Employee Stock Purchase Plan	276		276
Employee Stock Purchase Plan (in shares)		21
Stock-based compensation expense	4,583		4,583
Net loss	(46,315)				(46,315)
Other comprehensive loss	(92)			(92)
Balance at Dec. 31, 2015	103,986	$ 22	243,853	(97)	(139,792)
Balance (in shares) at Dec. 31, 2015		21,570
Issuance of Common Stock net of issuance costs	147,501	$ 10	147,491
Issuance of Common Stock net of issuance costs (in shares)		10,040
Exercise of stock options	167		167
Exercise of stock options (in shares)		30
Employee Stock Purchase Plan	476		476
Employee Stock Purchase Plan (in shares)		27
Stock-based compensation expense	6,770		6,770
Net loss	(71,894)				(71,894)
Other comprehensive loss	26			26
Balance at Dec. 31, 2016	187,032	$ 32	398,757	(71)	(211,686)
Balance (in shares) at Dec. 31, 2016		31,667
Exercise of stock options	$ 1,457		1,457
Exercise of stock options (in shares)	182	182
Employee Stock Purchase Plan	$ 453		453
Employee Stock Purchase Plan (in shares)		56
Stock-based compensation expense	4,741		4,741
Convertible debt	62,466		62,466
Net loss	(52,764)				(52,764)
Other comprehensive loss	(6)			(6)
Balance at Jun. 30, 2017	$ 203,379	$ 32	$ 467,874	$ (77)	$ (264,450)
Balance (in shares) at Jun. 30, 2017		31,905