Major Category of Assets Measured at Fair Value on Recurring Basis (Detail) (Fair Value, Measurements, Recurring, USD $)	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	$ 29,551,078
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	7,891,062
U.S. Government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	8,102,220
Corporate and other debt securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	13,557,796
Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	10,792,271
Quoted prices in active markets for identical assets (Level 1) | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	7,891,062
Quoted prices in active markets for identical assets (Level 1) | U.S. Government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	2,901,209
Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	18,758,807
Significant other observable inputs (Level 2) | U.S. Government and agency securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	5,201,011
Significant other observable inputs (Level 2) | Corporate and other debt securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	$ 13,557,796