Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities:
Net loss	$ (122,071)	$ (103,410)
Adjustments to reconcile net loss to cash flows from operating activities:
Depreciation and amortization	2,873	2,571
Amortization of premium on available-for-sale securities, loss from sale of available-for-sale securities and non-cash interest	394	613
Loss on abandonment of patents	24	132
Stock-based compensation	13,665	20,086
Changes in operating assets and liabilities, net:
Net increase in accounts receivable	(5)
Net (increase) decrease in other assets	(394)	8,695
Net increase (decrease) in accounts payable, accrued expenses, deferred revenue and other liabilities	1,542	(566)
Net cash used in operating activities	(103,972)	(71,879)
Cash flows from investing activities:
Purchase of property and equipment	(1,587)	(1,169)
Patent costs	(768)	(640)
Purchase of available-for-sale securities		(49,631)
Sale and maturity of available-for-sale securities	100,712	98,650
Net cash provided by investing activities	98,357	47,210
Cash flows from financing activities:
Proceeds from borrowings, net of debt issuance costs		19,734
Repayments of long-term debt and notes payable	(2,551)	(49)
Proceeds from exercise of options, purchase of stock under the Employee Stock Purchase Program and sales of common stock	39,681	971
Net cash provided by financing activities	37,130	20,656
Increase (decrease) in cash and cash equivalents	31,515	(4,013)
Cash and cash equivalents:
Beginning of period	80,304	73,551
End of period	111,819	69,538
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	828	37
Supplemental schedule of non-cash investing activities and financing activities:
Property and equipment included in accrued expenses	99
Accrual for senior secured term loan principal payment	833
Accrual for debt issuance costs related to the senior secured term loan	400	540
Patent costs included in accrued expenses	259	170
Accrual for offering costs related to the June 2016 equity offering	170
Shares withheld for taxes	$ 104
Capitalized interest		$ 99