Condensed Consolidated Statements of Changes in Redeemable Common Stock and Stockholders’ Equity (Deficit) - USD ($) $ in Thousands	Redeemable Common Stock	Class D Preferred Stock	Class C Preferred Stock	Class B-1 Preferred Stock	Employee Stock Options	Common Stock IPO	Common Stock Follow-On Offering	Common Stock Class B Note	Common Stock	Additional Paid-in Capital IPO	Additional Paid-in Capital Follow-On Offering	Additional Paid-in Capital Class B Note	Additional Paid-in Capital	Accumulated Deficit	IPO	Follow-On Offering	Class B Note	Total
Balance at the beginning of the period at Dec. 31, 2014	$ 560
Balance at the beginning of the period (in shares) at Dec. 31, 2014	418,000		1,262,000	2,226,000
Increase (Decrease) in Redeemable Common Stock
Issuance of redeemable common stock at fair value	$ 473
Issuance of redeemable common stock at fair value (in shares)	38,000	3,093,000	1,103,000	1,012,000
Balance at the end of the period at Dec. 31, 2015	$ 1,033
Balance at the end of the period (in shares) at Dec. 31, 2015	456,000	3,093,000	2,365,000	3,238,000
Balance at the beginning of the period at Dec. 31, 2014									$ 1				$ 17,643	$ (20,076)				$ (2,432)
Balance at the beginning of the period (in shares) at Dec. 31, 2014									6,472,000
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation - restricted stock													19,322
Stock based compensation—restricted stock																		19,322
Stock-based compensation - stock options													5,250					5,250
Stock-based compensation - stock warrants													359					359
Stock-based compensation – shares exchange													64,787					64,787
Stock-based compensation – share grants													5,000					5,000
Share exchanges													2,500					2,500
Conversion of convertible debt												$ 341
Exercise of stock options													521					521
Exercise of stock options (in shares)									207,000
Exercise of stock warrant																	$ 341
Exercise of stock warrant (in shares)								138,000
Net loss														(38,474)				(38,474)
Balance at the end of the period at Dec. 31, 2015									$ 1				115,723	(58,550)				57,174
Balance at the end of the period (in shares) at Dec. 31, 2015									6,817,000
Balance at the end of the period at Dec. 31, 2016	$ 0
Balance at the end of the period (in shares) at Dec. 31, 2016	0
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation - restricted stock													10,371					10,371
Stock based compensation—restricted stock (in shares)									1,751,000
Stock-based compensation - stock options													16,415					16,415
Shares conversion amount									$ 1				(1)
Shares converted (in shares)		(3,093,000)	(2,365,000)	(3,238,000)					8,696,000
Share conversion, converted to common stock	$ (1,033)												1,033					1,033
Share conversion, converted to common stock (in shares)	(456,000)								456,000
Exercise of stock options													430					430
Exercise of stock options (in shares)									84,000
Exercise of stock warrant													53					53
Exercise of stock warrant (in shares)									20,000
Issuance of stock						$ 1				$ 95,348	$ 148,319				$ 95,349	$ 148,319
Issuance of stock (in shares)						5,278,000	4,598,000
Net loss														(83,012)				(83,012)
Balance at the end of the period at Dec. 31, 2016		$ 0	$ 0	$ 0					$ 2				387,691	(141,562)				246,132
Balance at the end of the period (in shares) at Dec. 31, 2016		0	0	0					27,700,000
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock based compensation—restricted stock													659					659
Stock-based compensation - stock options													30,885					30,885
Exercise of stock options													3,689					3,689
Exercise of stock options (in shares)					(268,000)				265,000
Issuance of stock											$ 269,869		(443)			$ 269,869		(443)
Issuance of stock (in shares)							4,111,000		14,000
Net loss														(218,051)				(218,051)
Balance at the end of the period at Dec. 31, 2017									$ 2				$ 692,350	$ (359,613)				$ 332,740
Balance at the end of the period (in shares) at Dec. 31, 2017									32,090,000