CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities
Net loss	$ (94,176)	$ (27,255)	$ (17,917)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	655	171	187
Lease incentive	(34)	(34)	(34)
Stock-based compensation expense	5,787	2,209	22
Non cash interest expense		6	7
Change in fair value of derivative liability			7
Changes in operating assets and liabilities:
Accounts receivable	(2,129)
Inventories	(1,316)
Prepaid expenses and other assets	(923)	(659)	183
Refundable PDUFA fee		2,335	(2,335)
Accounts payable	5,569	1,298	990
Accrued expenses	6,570	362	943
Deferred revenue	4,944
Net cash used in operating activities	(75,053)	(21,567)	(17,947)
Investing activities
Purchase of intangible assets	(2,500)
Purchases of property and equipment	(477)	(362)	(8)
Net cash used in investing activities	(2,977)	(362)	(8)
Financing activities
Proceeds from issuance of convertible bridge note			5,000
Proceeds from issuances of common stock from public offerings, net of issuance costs of $845 and $2,408	137,340	72,029
Proceeds from issuances of common stock from employee stock purchase plans	442
Proceeds from notes payable, net of original note payoff			7,056
Proceeds from issuance of Series D convertible redeemable preferred stock, net of issuance costs of $193		44,807
Repayment of term note	(2,667)	(1,286)	(28)
Repayment of lease note payable		(59)	(62)
Restricted cash		(16)
Proceeds from the exercise of stock options	443	517	72
Net cash provided by financing activities	135,558	115,992	12,038
Net increase (decrease) in cash and cash equivalents	57,528	94,063	(5,917)
Cash and cash equivalents at beginning of period	95,697	1,634	7,551
Cash and cash equivalents at end of period	153,225	95,697	1,634
Supplemental disclosure of cash flow information
Cash paid for interest	284	353	181
Supplemental disclosure of non-cash activities
Acquisition of property and equipment in accrued expenses	$ 81
Preferred stock conversion to common stock		120,302
Extinguishment of preferred stock		31,184
Accruals of dividends and accretion to redemption value		24,572	3,300
Conversion of bridge note to preferred stock		5,000
Repayment of term note with proceeds of notes payable			944
Series C convertible redeemable preferred stock
Supplemental disclosure of non-cash activities
Accruals of dividends and accretion to redemption value		2,996	$ 960
Series D convertible redeemable preferred stock
Supplemental disclosure of non-cash activities
Accruals of dividends and accretion to redemption value		$ 1,245