Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities
Net loss	$ (87,748)	$ (36,555)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	729	27
Stock-based compensation	13,257	17,387
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(4,306)	(2,119)
Other long-term assets	(1,155)	(731)
Accounts payable	3,457	795
Accrued expenses	1,089	866
Accrued indemnification obligation	(1,675)
Net cash used in operating activities, Total	(76,352)	(20,330)
Cash flows from investing activities
Capital expenditures	(16,758)	(7,503)
Net cash used in investing activities, Total	(16,758)	(7,503)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Proceeds from issuance of common stock, net of issuance costs	270,256	98,170
Payments of deferred offering costs		(1,198)
Proceeds from exercise of stock options	461
Service-based restricted stock unit vesting	(417)
Proceeds from exercise of stock warrants		42
Net cash provided by financing activities, Total	270,300	97,014
Net (decrease) increase in cash and cash equivalents	177,190	69,181
Cash and cash equivalents, beginning of period	240,430	62,252
Cash and cash equivalents, end of period	417,620	131,433
Supplemental cash flow information:
Capital expenditures in accounts payable and accrued liabilities	4,936	$ 578
Accrued unpaid issuance costs associated with June 2017 public offering	$ 518