Average Market Price of Signature Common Stock and the Incremental Shares that Included in Diluted Shares Outstanding (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Average market price of Signature common stock	$ 11.89	$ 3.56	$ 7.76	$ 3.18
Anti-dilutive common stock equivalents:
Total anti-dilutive common stock equivalents	1,426,703	102,139	624,814	68,040
Unvested restricted stock
Anti-dilutive common stock equivalents:
Total anti-dilutive common stock equivalents	275,151	99,421	233,483	67,640
Common stock options
Anti-dilutive common stock equivalents:
Total anti-dilutive common stock equivalents	514,924	2,718	215,406	400
Warrants
Anti-dilutive common stock equivalents:
Total anti-dilutive common stock equivalents	636,628		175,925