CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating Activities:
Net loss	$ (77,252)	$ (24,370)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	1,954	1,309
Amortization of net premiums on marketable securities	146	427
Amortization of debt issuance costs	237	0
Deferred rent	(193)	(195)
Non-cash stock-based compensation	4,961	1,932
Other	98	146
Changes in operating assets and liabilities:
Restricted cash	1,278	297
Accounts receivable	1,926	(78)
Prepaid expenses and other assets	(1,289)	(2,491)
Accounts payable and accrued expenses	1,482	(7,574)
Deferred revenue	(1,644)	107
Other liabilities	(1,535)	0
Net cash used in operating activities	(69,831)	(30,490)
Investing Activities:
Capital expenditures	(5,517)	(4,864)
Proceeds from maturities of marketable securities	82,657	29,450
Purchases of marketable securities	(246,580)	(6,798)
Net cash provided by (used in) investing activities	(169,440)	17,788
Financing Activities:
Principal payments on capital leases	(19)	(16)
Principal payments on notes payable	(143)	(164)
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	193,619
Proceeds from the exercise of stock options and employee stock purchases	2,000	2,057
Net cash provided by financing activities	278,351	195,496
Effect of exchange rate on cash and cash equivalents	37	(79)
Net increase in cash and cash equivalents	39,117	182,715
Cash and cash equivalents at beginning of period	93,108	32,335
Cash and cash equivalents at end of period	132,225	215,050
Supplemental disclosure of non-cash activities:
Property and equipment purchases included in accounts payable and accrued expenses	3,180	3,118
Supplemental disclosure of cash flow information:
Cash payments of interest	$ 12	$ 31