CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Cash Flows from Operating Activities:
Net loss	$ (13,132)	$ (6,480)	$ (14,015)	$ (3,963)	$ (73,947)	$ (26,936)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation					164	156
Share-based compensation					911	935
Change in fair value of contingent consideration	3,600		7,200		46,600	9,900
Gain on sale of equipment					0	(5)
Changes in operating assets and liabilities:
Prepaid expenses and other assets					(421)	(1,169)
Accounts payable					1,216	484
Accrued expenses and other liabilities					1,761	1,453
Net Cash Used in Operating Activities					(23,716)	(15,182)	$ (22,800)
Cash Flows from Investing Activities:
(Purchases) sales of equipment					(137)
(Purchases) sales of equipment						5
Net Cash (Used in) Provided by Investing Activities					(137)	5
Cash Flows from Financing Activities:
Proceeds from issuance of common stock and common stock warrants, net of issuance costs					27,809	50,971
Proceeds from exercises of common stock warrants					3,434	7,315
Proceeds from exercises of stock options					45	56
Proceeds from sales of common stock under 2014 ESPP					8	21
Net Cash Provided by Financing Activities					31,296	58,363
Net Increase in Cash, Cash Equivalents and Restricted Cash					7,443	43,186
Cash, Cash Equivalents and Restricted Cash - Beginning of Period		$ 50,442		$ 14,690	50,442	14,690	14,690
Cash, Cash Equivalents and Restricted Cash - End of Period	$ 57,885		$ 57,876		57,885	$ 57,876	$ 50,442
Supplemental disclosure of non-cash operating activities:
Right-of-use assets related to the adoption of ASC 842					236
Cash paid for amounts included in the measurement of lease liabilities					$ 115