CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Operating Activities:
Net loss	$ (222,857)	$ (78,131)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	6,287	4,347
Amortization of net premiums on marketable securities	263	955
Amortization of debt issuance costs	949	0
Deferred rent	402	(554)
Lease incentives received	1,963	0
Non-cash stock-based compensation	15,380	9,278
Other	301	140
Changes in operating assets and liabilities:
Restricted cash	4,980	297
Accounts receivable	1,716	6,466
Prepaid expenses and other assets	(2,478)	(6,536)
Accounts payable and accrued expenses	6,396	(7,706)
Deferred revenue	(5,980)	105
Other liabilities	(1,541)	0
Net cash used in operating activities	(194,219)	(71,339)
Investing Activities:
Capital expenditures	(15,009)	(13,648)
Proceeds from maturities of marketable securities	284,871	137,107
Purchases of marketable securities	(327,750)	(154,288)
Net cash used in investing activities	(57,888)	(30,829)
Financing Activities:
Principal payments on capital leases	(53)	(49)
Principal payments on notes payable	(350)	(458)
Changes in restricted cash	(819)	(126)
Proceeds from issuance of convertible notes	325,000	0
Payments of costs related to issuance of convertible notes	(9,966)	0
Payments for capped call transactions and costs	(38,521)	0
Net proceeds from sales of common stock	0	204,275
Proceeds from the exercise of stock options and employee stock purchases	3,793	4,440
Net cash provided by financing activities	279,084	208,082
Effect of exchange rate on cash and cash equivalents	(137)	(105)
Net increase in cash and cash equivalents	26,840	105,809
Cash and cash equivalents at beginning of period	93,108	32,335
Cash and cash equivalents at end of period	119,948	138,144
Supplemental disclosure of non-cash activities:
Property and equipment purchases included in accounts payable and accrued expenses	2,060	2,390
Supplemental disclosure of cash flow information:
Cash payments of interest	$ 6,186	$ 79