CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Cash Flows from Operating Activities:
Net loss	$ (21,877)	$ (27,362)
Non-cash items:
Depreciation and amortization	2,089	1,863
Share-based compensation expense (income)	(4,385)	3,451
Amortization of premium on investments	304	847
Amortization of intangibles	265	265
Changes in operating assets and liabilities:
Accounts receivable	1,555	5,291
Unbilled revenue	110	(332)
Prepaid expenses and other current assets	157	(199)
Accounts payable	(1,939)	(1,453)
Accrued expenses	(3,037)	(1,423)
Deferred revenue	(1,687)	(1,041)
Other current liabilities	20	(19)
Other long-term liabilities	(151)	(97)
Net cash used in operating activities	(28,576)	(20,209)
Cash Flows from Investing Activities:
Purchases of property and equipment	(539)	(2,503)
Purchases of marketable securities	(15,694)	(34,365)
Proceeds from maturities of marketable securities	44,492	70,980
Net cash provided by investing activities	28,259	34,112
Cash Flows from Financing Activities:
Net proceeds from issuance of common stock under ATM facility	33,665
Proceeds from issuance of common stock under stock plans	2,911	1,841
Net cash provided by financing activities	36,576	1,841
Increase in cash and cash equivalents	36,259	15,744
Cash and cash equivalents, beginning of period	61,349	29,766
Cash and cash equivalents, end of period	$ 97,608	$ 45,510