Condensed Consolidated Statements of Cash Flows (USD $) In Thousands	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
Operating activities
Net income (loss)	$ 79,635	$ (29,867)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	765	643
Stock-based compensation	2,593	1,914
Non-cash interest expense	462	893
Deferred rent	(105)	(73)
Loss on disposal of property and equipment		1
Remeasurement of warrants to purchase convertible preferred stock		(713)
Amortization of premium on investments	1,633	22
Changes in operating assets and liabilities:
Accounts receivable	(28,379)	280
Prepaid expenses and other current assets	(4,441)	(4,637)
Other noncurrent assets	226	1,320
Restricted cash	(98)
Accounts payable	3,691	3,477
Accrued expenses	156	316
Deferred revenue	(10,641)	(2,508)
Net cash provided by (used in) operating activities	45,497	(28,932)
Investing activities
Purchases of property and equipment	(1,241)	(408)
Purchases of marketable securities	(200,749)	(77,021)
Proceeds from maturities and sales of marketable securities	77,836	6,000
Net cash used in investing activities	(124,154)	(71,429)
Financing activities
Proceeds from issuance of common stock, net of issuance costs	112,165	80,309
Proceeds from exercise of stock options and issuance of common stock	1,714	502
Proceeds from refinancing of loans payable		7,555
Principal payments on loans payable		(3,278)
Net cash provided by financing activities	113,879	85,088
Net increase (decrease) in cash and cash equivalents	35,222	(15,273)
Cash and cash equivalents at beginning of period	45,791	45,290
Cash and cash equivalents at end of period	81,013	30,017
Supplemental cash flow and noncash investing and financing
Issuance of warrants in conjunction with loan		780
Cash paid for interest	1,504	914
Cash paid for income taxes