Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Cash flows from operating activities
Net loss	$ (58,574)	$ (43,541)
Adjustments to reconcile net loss to net cash used in operating activities
Non-cash interest expense	470
Remeasurement of convertible preferred stock warrants		(587)
Depreciation and amortization	1,319	2,263
Stock-based compensation	5,416	2,749
Changes in operating assets and liabilities
Purchased premiums and interest on available-for-sale securities	(291)	(1,760)
Accounts receivable	(5,270)	486
Accounts payable, accrued expenses and other	11,386	(653)
Deferred revenues	(2,404)	553
Other assets and liabilities, net	2,518	48
Net cash used in operating activities	(45,430)	(40,442)
Cash flows from investing activities
Purchases of available-for-sale securities	(8,290)	(73,825)
Proceeds from sales and maturities of available-for-sale securities	49,010
Purchases of property and equipment	(3,305)	(891)
Other investing activities, net	(39)	(100)
Net cash (used in) provided by investing activities	37,376	(74,816)
Cash flows from financing activities
Proceeds from initial public offering, net of issuance costs		100,025
Proceeds from issuance of common stock	1,204	873
Proceeds from convertible notes issued by majority owned subsidiary, net of issuance costs	274
Payment of dividends on Series B convertible preferred stock		(4,003)
Other financing activities, net	(195)	(48)
Net cash provided by financing activities	1,283	96,847
Net decrease in cash and cash equivalents	(6,771)	(18,411)
Cash and cash equivalents, beginning of period	37,714	50,454
Cash and cash equivalents, end of period	30,943	32,043
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 stockholders' equity		2,748
Dividends on Series B convertible preferred stock declared but not paid		261
Issuance of derivative liability	35
Disposal of fully depreciated assets	77
Supplemental disclosure of cash flows
Cash paid for interest	$ 2,076