Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating activities:
Net loss	$ (66,060)	$ (61,577)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	253	78
Amortization of premium/discount on investments	389	287
Fair value of warrants issued for license	3,413
Changes in operating assets and liabilities:
Unbilled receivable	33,823
Prepaid expenses and other current assets	(9,019)	(1,311)
Other long-term assets	(79)
Accounts payable	8,173	2,830
Accrued expense	(1,547)	6,362
Deferred revenue	40,588	40,000
Deferred rent	380	1,337
Net cash provided by (used in) operating activities	14,836	(9,521)
Investing activities:
Purchase of equipment	(575)	(1,358)
Proceeds from the maturities of available for sale securities	54,118	64,874
Purchase of available for sale securities	(177,536)	(118,684)
Net cash used in investing activities	(123,993)	(55,168)
Financing activities:
Proceeds from the issuance of common stock, net of issuance costs	46,912	60,869
Proceeds from the sale of stock under employee stock purchase plan	125	105
Proceeds from the exercise of stock options	178	120
Payments on capital lease obligations	(3)	(6)
Net cash provided by financing activities	47,212	61,088
Decrease in cash and cash equivalents	(61,945)	(3,601)
Cash and cash equivalents at beginning of the period	187,335	49,778
Cash and cash equivalents at end of the period	125,390	46,177
Non-cash financing activities
Unpaid follow-on offering costs	137	131
Equity Awards
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation - equity awards	$ 4,522	$ 2,473