Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Cash flows from operating activities:
Net loss	$ (109,983)	$ (159,051)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	6,211	5,577
Share-based compensation expense	12,086	10,092
Write-down of inventory to net realizable value	8,894	0
Accretion of discount/premium on investment securities	466	887
Non-cash interest expense	788	937
Changes in assets and liabilities:
Accounts receivable and related party accounts receivable	(1,242)	(3,811)
Restricted cash		(500)
Prepaid expenses and other current assets	(84)	(3,447)
Inventory	272	(10,197)
Other assets	(116)	72
Accounts payable and accrued expenses	(7,691)	(10,098)
Accrued research and development costs	(1,177)	(718)
Deferred revenue	(1,164)	(2,379)
Deferred rent	(1,364)	(1,348)
Other liabilities		661
Net cash used in operating activities	(94,104)	(173,323)
Cash flows from investing activities:
Purchases of available-for-sale securities	(206,943)	(144,584)
Sales and maturities of available-for-sale securities	121,969	94,142
Purchases of property and equipment	(2,023)	(4,890)
Net cash used in investing activities	(86,997)	(55,332)
Cash flows from financing activities:
Proceeds from issuance of common stock	190,428	137,766
Proceeds from issuance of notes payable		175,000
Costs associated with issuance of notes payable		(7,717)
Proceeds from exercise of stock options and employee stock purchase plan	11,064	6,515
Payments on capital leases	(524)	(148)
Net cash provided by financing activities	200,968	311,416
Net increase in cash and cash equivalents	19,867	82,761
Cash and cash equivalents, beginning of period	75,490	136,700
Cash and cash equivalents, end of period	$ 95,357	$ 219,461