Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities
Net loss	$ (98,337)	$ (66,861)
Adjustments to reconcile net loss to net cash used in operating activities
Non-cash interest expense	2,341
Depreciation and amortization	1,926	2,943
Stock-based compensation	7,953	4,932
Other non-cash items	810	(587)
Changes in operating assets and liabilities
Purchased premiums and interest on available-for-sale securities	(1,535)	(1,760)
Accounts receivable	432	1,372
Accounts payable, accrued expenses and other	19,741	19
Deferred revenues	(4,738)	(2,001)
Other assets and liabilities, net	3,657	1,561
Net cash used in operating activities	(67,750)	(60,382)
Cash flows from investing activities
Purchases of available-for-sale securities	(78,699)	(73,825)
Proceeds from sales and maturities of available-for-sale securities	74,140	15,500
Purchases of property and equipment	(9,061)	(1,424)
Other investing activities, net	(56)	(100)
Net cash used in investing activities	(13,676)	(59,849)
Cash flows from financing activities
Proceeds from issuance of common stock, net of issuance costs	28,271	101,910
Proceeds from convertible notes issued by majority owned subsidiary, net of issuance costs	274
Proceeds from issuance of convertible senior notes, net of issuance costs	120,621
Payment of dividends on Series B convertible preferred stock	(3)	(4,176)
Other financing activities, net		(48)
Net cash provided by financing activities	149,163	97,686
Net (decrease) increase in cash and cash equivalents	67,737	(22,545)
Cash and cash equivalents, beginning of period	37,714	50,454
Cash and cash equivalents, end of period	105,451	27,909
Non-cash investing and financing activities
Conversion of convertible preferred stock to common stock		268,225
Conversion of convertible preferred stock warrants to common stock warrants		929
Reclassification of deferred financing costs to issuance costs	278	2,748
Value of equity premium on convertible senior notes, net of issuance costs, classified in Stockholders' Deficit	51,876
Dividends on Series B convertible preferred stock declared but not paid		88
Issuance of derivative liability	35
Disposal of fully depreciated assets	136
Changes in property and equipment in accounts payable and accrued expenses	1,761
Supplemental disclosure of cash flows
Cash paid for interest	$ 2,849