Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary of Significant Accounting Policies [Abstract]
Number of operating segments	2
Cash and cash equivalents [Abstract]
Cash and cash equivalents	$ 55,116,328	$ 63,077,178	$ 55,099,319	$ 81,948,482
Total cash and cash equivalents	55,116,328	63,077,178	55,099,319	81,948,482
Short-term investments [Abstract]
Held-to-maturity (less than one year to maturity)	10,535,741	20,270,954
Short-term investments	33,057,835	24,739,998
Short-term Investments [Member]
Short-term investments [Abstract]
Held-to-maturity (less than one year to maturity)	33,057,835	24,739,998
Other Investments [Member]
Short-term investments [Abstract]
Held-to-maturity (less than one year to maturity)	10,500,000	20,300,000
Minimum [Member] | Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term	3 months
Maximum [Member] | Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term	1 year
Commercial Paper [Member] | Short-term Investments [Member]
Short-term investments [Abstract]
Held-to-maturity (less than one year to maturity)	9,000,000	18,700,000
Commercial Paper [Member] | Minimum [Member] | Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term	1 month 6 days	9 days
Commercial Paper [Member] | Maximum [Member] | Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term	6 months	7 months 6 days
U.S. Agency Bonds [Member] | Short-term Investments [Member]
Short-term investments [Abstract]
Held-to-maturity (less than one year to maturity)	8,000,000	4,000,000
U.S. Agency Bonds [Member] | Other Investments [Member]
Short-term investments [Abstract]
Held-to-maturity (less than one year to maturity)	6,000,000	8,100,000
U.S. Agency Bonds [Member] | Minimum [Member] | Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term	2 months 12 days	13 days
U.S. Agency Bonds [Member] | Minimum [Member] | Other Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term	1 year 4 months 24 days	1 year 2 months 12 days
U.S. Agency Bonds [Member] | Maximum [Member] | Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term	10 months 24 days	8 months 12 days
U.S. Agency Bonds [Member] | Maximum [Member] | Other Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term	1 year 9 months 18 days	1 year 10 months 24 days
Corporate Bonds [Member] | Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term		7 months 6 days
Short-term investments [Abstract]
Held-to-maturity (less than one year to maturity)	10,100,000	2,000,000
Corporate Bonds [Member] | Other Investments [Member]
Short-term investments [Abstract]
Held-to-maturity (less than one year to maturity)		10,200,000
Corporate Bonds [Member] | Minimum [Member] | Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term	1 month 6 days
Corporate Bonds [Member] | Minimum [Member] | Other Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term		1 year 1 month 6 days
Corporate Bonds [Member] | Maximum [Member] | Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term	7 months 6 days
Corporate Bonds [Member] | Maximum [Member] | Other Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term		1 year 7 months 6 days
U.S. Treasuries [Member] | Short-term Investments [Member]
Short-term investments [Abstract]
Held-to-maturity (less than one year to maturity)	6,000,000
U.S. Treasuries [Member] | Other Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term		1 year 7 months 6 days
Short-term investments [Abstract]
Held-to-maturity (less than one year to maturity)	$ 4,500,000	$ 2,000,000
U.S. Treasuries [Member] | Minimum [Member] | Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term	6 months
U.S. Treasuries [Member] | Minimum [Member] | Other Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term	1 year 3 months 18 days
U.S. Treasuries [Member] | Maximum [Member] | Short-term Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term	9 months 18 days
U.S. Treasuries [Member] | Maximum [Member] | Other Investments [Member]
Cash and Cash Equivalents [Line Items]
Maturity term	1 year 7 months 6 days