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Fair Value Measurement of Assets and Liabilities - Fair Value of Short and Long-Term Investments Classified as Available for Sale Securities (Detail) (USD $)
Jun. 30, 2013
Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]    
Cost $ 96,967,434 $ 114,157,963
Gross Unrealized Gains 36,990 1,236,697
Gross Unrealized Losses (280,352) (90,035)
Estimated Fair Value 96,724,072 115,304,625
Cash and Cash Equivalents [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 27,716,592 23,030,970
Gross Unrealized Gains   3,400
Gross Unrealized Losses (4,583) (1,013)
Estimated Fair Value 27,712,009 23,033,357
Short-Term Investments [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 9,583,483 6,314,939
Gross Unrealized Gains 857 1,032
Gross Unrealized Losses (9,862) (287)
Estimated Fair Value 9,574,478 6,315,684
Long-Term Investments [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost   84,812,054
Gross Unrealized Gains   1,232,265
Gross Unrealized Losses   (88,735)
Estimated Fair Value   85,955,584
Money Market Funds [Member] | Cash and Cash Equivalents [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 27,716,592 23,030,970
Gross Unrealized Gains 0 3,400
Gross Unrealized Losses (4,583) (1,013)
Estimated Fair Value 27,712,009 23,033,357
Corporate Debt Securities [Member] | Short-Term Investments [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 5,604,611 6,314,939
Gross Unrealized Gains   1,032
Gross Unrealized Losses (9,862) (287)
Estimated Fair Value 5,594,749 6,315,684
Corporate Debt Securities [Member] | Long-Term Investments [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 36,759,140 45,089,831
Gross Unrealized Gains 8,196 630,807
Gross Unrealized Losses (218,300) (45,028)
Estimated Fair Value 36,549,036 45,675,610
Sovereign Debt Securities [Member] | Short-Term Investments [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 3,978,872  
Gross Unrealized Gains 857  
Estimated Fair Value 3,979,729  
Sovereign Debt Securities [Member] | Long-Term Investments [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 22,908,219 21,153,227
Gross Unrealized Gains 27,937 299,914
Gross Unrealized Losses (47,607)  
Estimated Fair Value 22,888,549 21,453,141
Asset Backed Securities [Member] | Long-Term Investments [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Cost 59,667,359 18,568,996
Gross Unrealized Gains 36,133 301,544
Gross Unrealized Losses (265,907) (43,707)
Estimated Fair Value $ 59,437,585 $ 18,826,833