CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN SHAREHOLDERS' EQUITY - 6 months ended Jun. 30, 2017 - USD ($) $ in Thousands	Total	Preferred Stock	Preferred Additional Paid-In Capital	Common Stock	Additional Paid-In Capital	Accumulated Deficit
BALANCE at Dec. 31, 2016	$ 221,009	$ 17	$ 162,494	$ 53	$ 265,355	$ (206,910)
Balance (in shares) at Dec. 31, 2016		17,000,000		52,628,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	7,978				7,978
Initial Public Offering net of costs (in shares)				13,250,000
Initial Public Offering, net of costs	170,141			$ 13	170,128
Conversion of preferred equity to common at IPO (in shares)		(17,000,000)		17,000,000
Conversion of preferred stock to common at Initial Public Offering	$ 0	$ (17)	(162,494)	$ 17	162,494
Exercise of stock options—net (in shares)	226,194			162,000
Exercise of stock options—net	$ 0			$ 0	0
Net loss	(19,431)					(19,431)
Balance (in shares) at Jun. 30, 2017		0		83,040,000
BALANCE at Jun. 30, 2017	$ 379,697	$ 0	$ 0	$ 83	$ 605,955	$ (226,341)