Shareholders Equity - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended				1 Months Ended				1 Months Ended	3 Months Ended		12 Months Ended	1 Months Ended
	Jul. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Mar. 28, 2012	Oct. 31, 2010 Vulcan Incorporated Warrants	Oct. 31, 2010 Vulcan Incorporated Warrant 1	Oct. 31, 2010 Vulcan Incorporated Warrant 2	Oct. 31, 2010 Vulcan Incorporated Warrant 3	Jul. 31, 2012 Public Offering	Sep. 30, 2012 Public Offering	Dec. 31, 2011 Warrants to purchase common stock	Dec. 31, 2012 At-the-market Sales Agreement	May 31, 2011 Equity Line Of Credit Facility Agreement	May 31, 2011 Equity Line Of Credit Facility Agreement Minimum	May 31, 2011 Equity Line Of Credit Facility Agreement Maximum	Dec. 31, 2012 Equity Line Financing Facility
Class of Stock [Line Items]
Maximum potential value from stock issuance under at-the-market sales agreement													$ 60,000,000
Sales Commission													2.00%
Maximum potential value of stock issuance under equity line financing facility														40,000,000			40,000,000
Term of equity line financing facility														24 months
Share Purchase price discount rate based on minimum price specified															3.00%	6.00%
Minimum trading days required between each draw down period														5 days
Maximum shares issuable under equity line financing facility																4,427,562
Common stock share price after discount, per share															$ 5.02
Acquisition fee as percentage of contract purchase price														0.50%
Public offering, number of shares of common stock sold										3,365,854	3,365,854
Public offering, common stock price per share										$ 10.25
Underwriting discounts and other offering expenses	2,200,000
Public offering, net proceeds		32,306,000								32,300,000
Number Of Warrants Issued Common Stock						3
Shares of common stock to purchase by warrant					197,478	133,333	133,333	133,333	133,333			609,016
Exercise Price of warrants					12.25		20	30	40
Warrant expiration date					Mar. 29, 2013	Oct. 21, 2015
Fair value of warrants		511,000		994,000		994,000
Change in fair value of warrants		$ 511,000
Weighted-average exercise prices			$ 23.85