Fair Value Measurements (Details) - Summary of Assets and Liabilities Measured at Fair Value (USD $)	Sep. 30, 2013		Dec. 31, 2012
Description:
Cash and cash equivalents	$ 39,625,879	[1]	$ 23,845,360	[1]
Restricted cash	1,301,000	[1]	1,301,000	[1]
Marketable securities	17,434,880	[2]	35,394,318	[2]
Total at fair value	58,361,759		60,540,678
Fair Value, Inputs, Level 1 [Member]
Description:
Cash and cash equivalents	39,625,879	[1]	23,845,360	[1]
Restricted cash	1,301,000	[1]	1,301,000	[1]
Marketable securities	15,854,880	[2]	33,854,318	[2]
Total at fair value	56,781,759		59,000,678
Fair Value, Inputs, Level 2 [Member]
Description:
Cash and cash equivalents	0	[1]	0	[1]
Restricted cash	0	[1]	0	[1]
Marketable securities	0	[2]	0	[2]
Total at fair value	0		0
Fair Value, Inputs, Level 3 [Member]
Description:
Cash and cash equivalents	0	[1]	0	[1]
Restricted cash	0	[1]	0	[1]
Marketable securities	1,580,000	[2]	1,540,000	[2]
Total at fair value	$ 1,580,000		$ 1,540,000

[1] Cash and cash equivalents and restricted cash, totaling approximately $40.9 million as of September 30, 2013 and $25.1 million as of December 31, 2012, consists primarily of money market funds and checking accounts for which we determine fair value through quoted market prices.

[2] Marketable securities consist of liquid short-term U.S. Treasuries, government agencies, certificates of deposit (insured up to FDIC limits), investment grade corporate and municipal bonds and corporate floating rate notes for which we determine fair value through quoted market prices. Marketable securities also consist of two municipal ARS issued by the District of Columbia having a fair value totaling approximately $1.6 million as of September 30, 2013 and approximately $1.5 million as of December 31, 2012. Historically, the fair value of ARS investments approximated par value due to the frequent resets through the auction process. Due to events in credit markets, the auction events, which historically have provided liquidity for these securities, have been unsuccessful. The result of a failed auction is that these ARS holdings will continue to pay interest in accordance with their terms at each respective auction date; however, liquidity of the securities will be limited until there is a successful auction, the issuer redeems the securities, the securities mature or until such time as other markets for these ARS holdings develop. For each of our ARS, we evaluate the risks related to the structure, collateral and liquidity of the investment, and forecast the probability of issuer default, auction failure and a successful auction at par, or a redemption at par, for each future auction period. Temporary impairment charges are recorded in accumulated other comprehensive (loss) income, whereas other-than-temporary impairment charges are recorded in our consolidated statement of operations. As of September 30, 2013, the Company determined there was a decline in the fair value of its ARS investments of approximately $270 thousand from its cost basis, which was deemed temporary and was included within accumulated other comprehensive loss. The Company used both a discounted cash flow and market approach model to determine the estimated fair value of its investment in ARS. The assumptions used in preparing the discounted cash flow model include estimates for interest rate, timing and amount of cash flows and expected holding period of ARS.