Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities:
Net loss	$ (31,470)	$ (20,151)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	457	419
Issuance of common stock for technology		1,411
Stock-based compensation	2,653	1,419
Amortization of debt discount	97	168
Change in fair value of preferred stock warrant liability		(29)
Amortization of premiums and accretion of discounts of investment securities, available-for-sale	397	192
Deferred rent	(154)	(144)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	394	(1,497)
Accounts payable and accrued expenses	1,147	717
Net cash used in operating activities	(26,479)	(17,495)
Cash flows from investing activities:
Purchase of property and equipment	(490)	(163)
Purchases of available-for-sale investment securities	(21,924)	(84,927)
Maturities of available-for-sale investment securities	40,651	1,954
Net cash provided by (used in) investing activities	18,237	(83,136)
Cash flows from financing activities:
Issuance of preferred stock for cash, net of issuance costs		75,617
Issuance of common stock through initial public offering, net of offering costs		77,246
Proceeds from issuance of common stock through option exercises	19	533
Proceeds from issuance of common stock pursuant to employee stock purchase plan	75
Repayments on notes payable to bank	(1,686)	(1,598)
Repayments of convertible debt		(2,000)
Net cash (used in) provided by financing activities	(1,592)	149,798
Net change in cash and cash equivalents	(9,834)	49,167
Cash and cash equivalents at beginning of the period	53,025	13,899
Cash and cash equivalents at end of the period	$ 43,191	63,066
Supplemental schedule of noncash investing and financing activities:
Initial public offering costs included in accounts payable		$ 344