Average Market Price of Common Stock and the Incremental Shares that were Potentially Dilutive (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Average market price of Signature common stock	$ 10.43	$ 4.70
Potentially dilutive common stock equivalents:
Total potentially dilutive common stock equivalents	1,025,553	157,690
Unvested Restricted Stock
Potentially dilutive common stock equivalents:
Total potentially dilutive common stock equivalents	34,151	135,170
Common Stock Options
Potentially dilutive common stock equivalents:
Total potentially dilutive common stock equivalents	476,267	22,520
Warrants
Potentially dilutive common stock equivalents:
Total potentially dilutive common stock equivalents	515,135