Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
CASH FLOWS USED IN OPERATING ACTIVITIES:
Net loss	$ (183,220)	$ (130,084)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,385	371
Amortization of premium (discount) on marketable securities, net	(100)	797
Amortization of debt discount and debt issuance costs	1,568	0
Stock-based compensation	28,785	18,702
Changes in operating assets and liabilities:
Inventory	(3,074)	0
Accounts receivable, net	(11,682)	0
Prepaid expenses and other current assets	(5,493)	3,308
Other long-term assets	(7)	(291)
Accounts payable	(2,414)	(3,563)
Accrued expenses and other current liabilities	7,327	7,284
Other non-current liabilities	(166)	402
Net cash used in operating activities	(167,091)	(103,074)
CASH FLOWS (USED IN) PROVIDED BY INVESTING ACTIVITIES:
Purchases of property and equipment	(2,950)	(2,125)
Payments for capitalized milestones	(8,712)	0
Purchases of marketable securities	(117,441)	(225,497)
Sales and maturities of marketable securities	170,208	367,141
Net cash provided by investing activities	41,105	139,519
CASH FLOWS PROVIDED BY FINANCING ACTIVITIES:
Proceeds from exercise of stock options	16,167	2,442
Proceeds from issuance of convertible debt	305,000	0
Payment of debt issuance costs	(9,360)	0
Proceeds from issuance of shares under employee stock purchase plan	2,550	0
Net cash provided by financing activities	314,357	2,442
NET INCREASE IN CASH AND CASH EQUIVALENTS	188,371	38,887
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	258,567	159,678
CASH AND CASH EQUIVALENTS AT END OF PERIOD	446,938	198,565
SUPPLEMENTAL DISCLOSURES:
Cash paid for income taxes	26	0
Property and equipment purchases in accrued expenses at period end	$ 487	$ 406