CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating Activities:
Net loss	$ (156,603)	$ (45,011)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	4,066	2,795
Amortization of net premiums on marketable securities	286	593
Amortization of debt issuance costs	593	0
Deferred rent	(164)	(365)
Lease incentives received	1,963	0
Non-cash stock-based compensation	10,218	4,514
Other	197	78
Changes in operating assets and liabilities:
Restricted cash	2,370	297
Accounts receivable	1,952	5,966
Prepaid expenses and other assets	(888)	(3,449)
Accounts payable and accrued expenses	9,028	(8,339)
Deferred revenue	(3,331)	109
Other liabilities	(1,550)	0
Net cash used in operating activities	(131,863)	(42,812)
Investing Activities:
Capital expenditures	(11,046)	(9,240)
Proceeds from maturities of marketable securities	151,217	63,350
Purchases of marketable securities	(290,630)	(75,729)
Net cash used in investing activities	(150,459)	(21,619)
Financing Activities:
Principal payments on capital leases	(37)	(33)
Principal payments on notes payable	(246)	(315)
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	197,093
Proceeds from the exercise of stock options and employee stock purchases	2,374	2,815
Net cash provided by financing activities	278,604	199,560
Effect of exchange rate on cash and cash equivalents	5	(80)
Net increase (decrease) in cash and cash equivalents	(3,713)	135,049
Cash and cash equivalents at beginning of period	93,108	32,335
Cash and cash equivalents at end of period	89,395	167,384
Supplemental disclosure of non-cash activities:
Property and equipment purchases included in accounts payable and accrued expenses	2,712	2,165
Sale of common stock under the Sales Agreement not settled at quarter-end	0	679
Supplemental disclosure of cash flow information:
Cash payments of interest	$ 21	$ 57