CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash Flows from Operating Activities:
Net loss	$ (54,149)	$ (82,619)
Non-cash items:
Depreciation and amortization	5,799	5,663
Share-based compensation expense	6,787	10,515
Amortization of premium on investments	987	1,855
Amortization of intangibles	796	796
Changes in operating assets and liabilities:
Accounts receivable	(3,633)	5,446
Unbilled revenue	940	357
Prepaid expenses and other current assets	136	(300)
Restricted cash	59
Accounts payable	(1,714)	(3,157)
Accrued expenses	3,779	461
Deferred revenue	(6,572)	(2,788)
Other current liabilities	25	(4)
Other long-term liabilities	(422)	(311)
Net cash used in operating activities	(47,182)	(64,086)
Cash Flows from Investing Activities:
Purchases of property and equipment	(2,747)	(5,907)
Purchases of marketable securities	(281,500)	(68,805)
Proceeds from maturities of marketable securities	105,844	161,280
Net cash (used in) / provided by investing activities	(178,403)	86,568
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	23,329	2,628
Purchase of treasury stock	(2,048)
Net cash provided by financing activities	234,223	2,628
Increase in cash and cash equivalents	8,638	25,110
Cash and cash equivalents, beginning of period	61,349	29,766
Cash and cash equivalents, end of period	$ 69,987	$ 54,876