Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Operating activities
Net loss	$ (15,848)	$ (10,144)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	723	537
Stock-based compensation expense	753	189
Deferred rent	(36)	(17)
Deferred taxes		3,317
(Accretion) amortization of (discount) premium on investments	(9)	167
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(2,690)	72
Accounts payable	(271)	(869)
Accrued expenses and other liabilities	1,845	770
Income taxes payable	266	(8,006)
Deferred revenue	(12,536)	(12,536)
Net cash used in operating activities	(27,803)	(26,520)
Investing activities
Purchases of marketable securities	(23,195)	(50,649)
Proceeds from maturities and sales of marketable securities	38,086	55,884
Purchases of property and equipment	(976)	(308)
Net cash provided by investing activities	13,915	4,927
Financing activities
Net proceeds from stock option exercises and issuance of common and restricted common stock	72	54
Net cash provided by financing activities	72	54
Net decrease in cash and cash equivalents	(13,816)	(21,539)
Cash and cash equivalents at beginning of the period	91,297	117,661
Cash and cash equivalents at end of the period	77,481	96,122
Supplemental cash flow information
Cash paid for income taxes		$ 3,500