Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities:
Net loss	$ (59,770)	$ (61,559)
Adjustments to reconcile net income to cash flows from operating activities:
Depreciation and amortization	1,397	1,280
Amortization of premium on available-for-sale securities and non-cash interest	242	315
Loss on abandonment of patents	15	131
Stock-based compensation	6,835	14,156
Changes in operating assets and liabilities, net:
Net increase in accounts receivable	(13)
Net (increase) decrease in other assets	(3,180)	7,413
Net decrease in accounts payable, accrued expenses, deferred revenue and other liabilities	(6,214)	(5,084)
Net cash used in operating activities	(60,688)	(43,348)
Cash flows from investing activities:
Purchase of property and equipment	(1,168)	(532)
Patent costs	(410)	(391)
Maturity of available-for-sale securities	21,000	44,750
Net cash provided by investing activities	19,422	43,827
Cash flows from financing activities:
Repayments of long-term debt and notes payable	(2,525)	(25)
Proceeds from exercise of options and purchase of stock under the Employee Stock Purchase Program	1,488	431
Net cash (used in) provided by financing activities	(1,037)	406
(Decrease) increase in cash and cash equivalents	(42,303)	885
Cash and cash equivalents:
Beginning of period	80,304	73,551
End of period	38,001	74,436
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	409	18
Supplemental schedule of non-cash investing activities and financing activities:
Property and equipment included in accrued expenses	19	45
Patent costs included in accrued expenses	192	100
Shares withheld for taxes	$ 44
Capitalized interest		$ 99