Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	4 Months Ended	12 Months Ended			88 Months Ended
	Dec. 31, 2012	Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2010	Dec. 31, 2012
Cash flows from operating activities:
Net loss	$ (19,292)	$ (38,644)	$ (37,195)	$ (18,928)	$ (135,938)
Adjustments to reconcile net loss to net cash used in operating activities:
Employee stock-based compensation expense	2,230	4,487	1,920	217	10,068
Consultant stock-based compensation expense	9	72	197	78	764
Fair value adjustment of common stock warrants	1,484	3,173	16,301	5,895	26,853
Amortization of intangible assets	49	146	153	152	746
Depreciation of fixed assets	42	65	78	72	608
Unrealized gain (loss) on short-term investments	64	0	0	0	64
Write-off of intangible assets and other intellectual property	0	900	108	0	1,249
Amortization of capitalized finder's fee	0	0	0	0	102
Capitalized acquisition costs previously expensed	0	0	0	0	38
Changes in assets and liabilities:
Prepaid expenses and other	1,501	(2,695)	(130)	(79)	(1,510)
Intangible assets	0	0	0	0	(150)
Deposits	79	0	(2)	(3)	(26)
Accounts payable	3,081	754	210	24	4,682
Accrued liabilities	(502)	403	1,119	(2)	1,470
Deferred rent	(8)	(10)	22	3	6
Net cash used in operating activities	(11,263)	(31,349)	(17,219)	(12,571)	(90,974)
Cash flows from investing activities:
Purchase of fixed assets	(55)	(378)	(50)	581	581
Cash acquired in 2009 Merger	0	0	0	(20)	(980)
Purchase of short-term investments	(6,853)	(45,307)	0	0	(52,160)
Sale of short-term investments		30,000	0	0	30,000
Change in restricted cash	6	(54)	(114)	0	(163)
Net cash used in investing activities	(6,902)	(15,739)	(164)	561	(22,722)
Cash flows from financing activities:
Proceeds from the sale of common stock	0	46,000	0	22,555	85,941
Proceeds from the sale of common stock under an equity line	0	0	6,740	4,900	11,640
Proceeds from the sale of common stock under an ATM agreement	6,157	7,684	0	0	13,841
Proceeds from the exercise of common stock warrants	1,843	5,013	8,913	475	22,754
Proceeds from the exercise of common stock options	192	366	96	64	727
Proceeds from note payable	25,000	0	0	0	25,000
Fundraising costs	(210)	(3,528)	0	(2,720)	(8,065)
Deferred offering costs	25	18	(152)	0	43
Proceeds from the sale of common stock to initial investors	0	0	0	0	310
Debt issuance costs	(1,959)	0	0	0	(1,959)
Principal payments on capital lease	(2)	(5)	(5)	(4)	(25)
Interest payment on note payable	(83)	0	0	0	(83)
Net cash provided by financing activities	30,963	55,548	15,592	25,270	150,124
Foreign currency translation adjustment	(65)	(52)	10	(8)	(115)
Net increase (decrease) in cash and cash equivalents	12,733	8,408	(1,781)	13,252	36,313
Cash and cash equivalents, beginning of period	23,580	15,172	16,954	3,702	0
Cash and cash equivalents, end of period	36,313	23,580	15,172	16,954	36,313
Supplemental cash flow information:
Interest Paid	83	3	2	4	100
Supplemental disclosure of non-cash financing activities:
Warrants issued in connection with financings				9,677	16,310
Initial fair value of warrants issued to placement agents in connection with financings				209	209
Common stock and warrants issued in connection with reverse merger				4,417	4,417
Common stock issued as fee for equity line	0	0	519	309	828
Fair value of warrant liability reclassified to equity upon exercise	2,345	9,482	8,506	0	20,333
Acquisition of equipment in exchange for capital lease	0	13	14	0	48
Notes receivable issued in exchange for common stock				0	110
Common stock issued for a finder's fee				0	102
Common stock issued in asset purchase					$ 2,899