Cash, Cash Equivalents, and Investments - Summary of Cash, Cash Equivalents and Held-to-Maturity Investments by Type (Detail) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	$ 48,336,952	$ 37,807,749
Gross Unrealized Gains	7,784
Gross Unrealized Losses	(8,606)	(1,488)
Fair Value	48,336,130	37,806,261
Cash and Money Market Funds [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	34,905,493	36,126,791
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value	34,905,493	36,126,791
State and Municipal Obligations [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	8,587,008
Gross Unrealized Gains	7,784
Gross Unrealized Losses	(9)
Fair Value	8,594,783
Corporate Bonds [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	2,962,150	958
Gross Unrealized Gains
Gross Unrealized Losses	(8,557)
Fair Value	2,953,593	958
Certificates of Deposit [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Amortized Cost	1,882,301	1,680,000
Gross Unrealized Gains
Gross Unrealized Losses	(40)	(1,488)
Fair Value	$ 1,882,261	$ 1,678,512