Consolidated Statement of Stockholders' Equity (Deficit) (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	4 Months Ended	12 Months Ended
	Dec. 31, 2012	Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2010	Aug. 31, 2009	Aug. 31, 2008	Aug. 31, 2006	Sep. 07, 2005
Condensed Consolidated Statement of Stockholders' Equity (Deficit) [Abstract]
Issuance of common stock to founders, price per share								$ 0.004
Common stock issued in specified period pursuant to a stock purchase agreement, specified price one							$ 0.43
Common stock issued in specified period pursuant to a stock purchase agreement, specified price two							$ 0.86
Common stock issued on specified date net of fundraising costs, specified price							$ 2.57
Fundraising costs of common stock issued							$ 218
Issuance of common stock and warrants under private placement, specified price				$ 3.075	$ 1.37	$ 2.14
Fundraising costs of common stock and warrants issued under private placement				1,458	294	944
Issuance of common stock pursuant to an equity line facility, specified price			$ 3.35	$ 2.26
Fundraising costs and commitment shares for issuance of common stock pursuant to an equity line facility			174	533
Issuance of common stock and warrants in a registered direct financing, specified price				$ 2.00
Fundraising costs of common stock and warrants issued in a registered direct financing				1,247
Issuance of common stock pursuant to a follow-on public offering, specified price		$ 4.00
Fundraising costs for issuance of common stock pursuant to a follow-on public offering		3,168
Issuance of common stock pursuant to an at-the-market financing facility, specified price	$ 5.34	$ 5.10
Fundraising costs for issuance of common stock pursuant to an at-the-market financing facility	$ 185	$ 360