CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash Flows from Operating Activities:
Net loss	$ (24,099)	$ (53,518)
Non-cash items:
Depreciation and amortization	3,963	3,637
Share-based compensation expense	2,231	7,116
Amortization of premium on investments	563	1,449
Amortization of intangibles	530	530
Changes in operating assets and liabilities:
Accounts receivable	(26,300)	4,527
Unbilled revenue	509	878
Prepaid expenses and other current assets	934	867
Accounts payable	(5,538)	(2,322)
Accrued expenses	6,997	(238)
Deferred revenue	(4,130)	(1,901)
Other current liabilities	61
Other long-term liabilities	(301)	(196)
Net cash used in operating activities	(44,580)	(39,171)
Cash Flows from Investing Activities:
Purchases of property and equipment	(1,360)	(4,718)
Purchases of marketable securities	(68,040)	(64,284)
Proceeds from maturities of marketable securities	92,334	139,415
Net cash provided by investing activities	22,934	70,413
Cash Flows from Financing Activities:
Proceeds from public offering of common stock, net of issuance costs	148,439
Net proceeds from issuance of common stock under ATM facilities	64,503
Proceeds from issuance of common stock under stock plans	21,210	1,911
Purchase of treasury stock	(2,048)
Net cash provided by financing activities	232,104	1,911
Increase in cash and cash equivalents	210,458	33,153
Cash and cash equivalents, beginning of period	61,349	29,766
Cash and cash equivalents, end of period	$ 271,807	$ 62,919