Average Market Price of Signature Common Stock and the Incremental Shares that Included in Diluted Shares Outstanding (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Average market price of Signature common stock	$ 0.65	$ 0.31	$ 0.56	$ 0.30
Anti-dilutive common stock equivalents:
Total anti-dilutive common stock equivalents	2,931,363	802,198	2,161,148	535,226
Unvested restricted stock
Anti-dilutive common stock equivalents:
Total anti-dilutive common stock equivalents	2,190,388	798,606	1,838,624	535,226
Common stock options
Anti-dilutive common stock equivalents:
Total anti-dilutive common stock equivalents	740,975	3,592	322,524
Warrants
Anti-dilutive common stock equivalents:
Total anti-dilutive common stock equivalents