Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities
Net loss	$ (251,408)	$ (171,012)	$ (92,362)
Adjustments to reconcile net loss to net cash used in operating activities:
Acquired in-process research and development	2,000	24,900	1,940
Depreciation & amortization expense	1,037	349	179
Stock-based compensation expense	25,914	11,683	7,759
Amortization of Financing Costs and Discounts	9,360	2,249
Loss on disposal of property and equipment		80
Changes in operating assets and liabilities:
Accounts receivable	(679)
Inventories	(1,106)
Other assets	(2,128)	2,327	(3,112)
Accounts payable	1,924	4,220	(1,301)
Accrued expenses	19,646	6,209	1,996
Deferred revenue	788
Other liabilities	121	1,510	13
Net cash used in operating activities	(194,531)	(117,485)	(84,888)
Investing activities
Acquisition of product candidate and technology licenses and milestone payments	(17,000)	(24,900)	(1,940)
Purchase of property and equipment	(2,305)	(1,011)	(400)
Change in restricted cash	(500)
Net cash used in investing activities	(19,805)	(25,911)	(2,340)
Financing activities
Proceeds from Debt, Net of Issuance Costs		194,698
Purchase of capped call options		(20,829)
Proceeds from sale of common stock, net of issuance costs	179,753	94,199	91,312
Proceeds from exercise of stock options	7,239	1,663	634
Proceeds from issuance of common stock under Employee Stock Purchase Plan	830	249	147
Payment of minimum tax withholding on share-based awards	(201)	(33)
Net cash provided by financing activities	187,621	269,947	92,093
Increase/(decrease) in cash and cash equivalents	(26,715)	126,551	4,865
Cash and cash equivalents at beginning of period	256,861	130,310	125,445
Cash and cash equivalents at end of period	230,146	$ 256,861	$ 130,310
Non-cash investing and financing activities
Stock option exercise proceeds receivable as of period end	691
Purchase of property and equipment - cash not paid as of period end	238
Supplemental disclosure of cash flow information
Interest Paid	$ 6,071