Condensed Consolidated Statements of Changes in Redeemable Convertible Preferred Stock and Stockholders' Deficit Statement - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Redeemable convertible preferred stock beginning balance at Dec. 31, 2015	$ 599,915
Redeemable convertible preferred stock beginning balance (in shares) at Dec. 31, 2015	55,422,002
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	$ 55,501
Redeemable convertible preferred stock ending balance at Dec. 31, 2016	$ 655,416
Redeemable convertible preferred stock ending balance (in shares) at Dec. 31, 2016	55,422,002
Common stock, outstanding, beginning balance (in shares) at Dec. 31, 2015		14,059,601
Total stockholders' deficit, beginning balance at Dec. 31, 2015	$ (495,713)	$ 14	$ 0	$ (495,727)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)		627,423
Exercise of stock options	1,495	$ 1	1,494
Stock-based compensation	8,512		8,512
Accretion of redeemable convertible preferred stock	(55,502)		(10,006)	(45,496)
Net income (loss)	$ (22,526)			(22,526)
Common stock, outstanding, ending balance (in shares) at Dec. 31, 2016	14,988,646	14,687,024
Total stockholders' deficit, ending balance at Dec. 31, 2016	$ (563,734)	$ 15	0	(563,749)
Increase (Decrease) in Stockholders' Equity
Cumulative stock-based compensation adjustment	0		522	(522)
Accretion of redeemable convertible preferred stock	135,690
Redeemable convertible preferred stock ending balance at Jun. 30, 2017	$ 791,106
Redeemable convertible preferred stock ending balance (in shares) at Jun. 30, 2017	55,422,002
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)	301,622	301,622
Exercise of stock options	$ 1,017	$ 0	1,017
Stock-based compensation	5,451		5,451
Accretion of redeemable convertible preferred stock	(135,690)		(6,990)	(128,700)
Net income (loss)	$ (23,762)			(23,762)
Common stock, outstanding, ending balance (in shares) at Jun. 30, 2017	14,687,024	14,988,646
Total stockholders' deficit, ending balance at Jun. 30, 2017	$ (716,718)	$ 15	$ 0	$ (716,733)