Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash flows from operating activities
Net loss	$ (66,861)	$ (61,455)
Adjustments to reconcile net loss to net cash used in operating activities
Remeasurement of convertible preferred stock warrants	(587)	742
Amortization of premium on available-for-sale securities	810
Amortization of deferred lease benefits and tax incentives	(903)	(567)
Depreciation and amortization	3,036	4,029
Stock-based compensation	4,932	5,573
Changes in operating assets and liabilities
Purchased premiums and interest on available-for-sale securities	(1,760)
Accounts receivable	1,372	(1,584)
Accounts payable	(3,885)	3,446
Accrued expenses and other	3,904	3,583
Deferred revenues	(2,001)	1,734
Other assets and liabilities, net	1,561	(1,863)
Net cash used in operating activities	(60,382)	(46,362)
Cash flows from investing activities
Purchases of available-for-sale securities	(73,825)
Proceeds from maturities of available-for-sale securities	15,500
Purchases of property and equipment	(1,424)	(2,468)
Other investing activities, net	(100)	8
Net cash used in investing activities	(59,849)	(2,460)
Cash flows from financing activities
Proceeds from initial public offering, net of offering costs	100,025
Proceeds from issuance of convertible preferred stock, net of offering costs		76,949
Proceeds from exercise of stock options	1,859	786
Proceeds from exercise of stock warrants	26
Principal payments on capital lease obligations	(48)	(394)
Payment of dividends on Series B convertible preferred stock	(4,176)
Net cash provided by financing activities	97,686	77,341
Net increase (decrease) in cash and cash equivalents	(22,545)	28,519
Cash and cash equivalents, beginning of period	50,454	30,713
Cash and cash equivalents, end of period	27,909	59,232
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	88
Supplemental disclosure of cash flows
Cash paid for interest		$ 12