Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities
Net loss	$ (387,472)	$ (251,408)	$ (171,012)
Adjustments to reconcile net loss to net cash used in operating activities:
Acquired in-process research and development	18,940	2,000	24,900
Depreciation and amortization expense	3,113	1,037	349
Stock-based compensation expense	48,455	25,914	11,683
Non-cash interest expense	10,450	9,360	2,249
Loss on disposal of property and equipment			80
Changes in operating assets and liabilities:
Accounts receivable	(4,664)	(679)
Inventories	(13,594)	(1,106)
Other assets	(7,685)	(2,128)	2,327
Accounts payable	(2,835)	1,924	4,220
Accrued expenses	31,897	19,646	6,209
Deferred revenues	14,501	788
Other liabilities	1,223	121	1,510
Net cash used in operating activities	(287,671)	(194,531)	(117,485)
Investing activities
Acquisition of product candidate and technology licenses and milestone payments	(18,940)	(17,000)	(24,900)
Purchase of property and equipment	(2,895)	(2,305)	(1,011)
Change in restricted cash	(1,489)	(500)
Net cash used in investing activities	(23,324)	(19,805)	(25,911)
Financing activities
Proceeds from issuance of convertible notes, net of issuance costs			194,698
Purchase of capped call options			(20,829)
Proceeds from sales of common stock, net of issuance costs	838,099	179,753	94,199
Proceeds from exercise of stock options	26,556	7,239	1,663
Proceeds from issuance of common stock under Employee Stock Purchase Plan	2,229	830	249
Payment of minimum tax withholdings on share-based awards		(201)	(33)
Net cash provided by financing activities	866,884	187,621	269,947
Increase in cash and cash equivalents	555,731	(26,715)	126,551
Cash and cash equivalents at beginning of period	230,146	256,861	130,310
Cash and cash equivalents at end of period	785,877	230,146	$ 256,861
Non-cash investing and financing activities
Purchase of property and equipment - cash not paid as of period end	230	238
Effect of Exchange Rate on Cash and Cash Equivalents	(158)
Stock option exercise proceeds receivable as of period end	93	691
Noncash or Part Noncash Acquisition, Fixed Assets Acquired	2,230
Supplemental cash flow information
Cash paid for interest	$ 6,038	$ 6,071