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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 1

-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

-Topic 210

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-Section S99

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-Topic 210

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-Paragraph 1

-Subparagraph (a)

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-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 4

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The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle).

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Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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Investments which are intended to be sold in the short term (usually less than one year or the normal operating cycle, whichever is longer) including trading securities, available-for-sale securities, held-to-maturity securities, and other short-term investments not otherwise listed in the existing taxonomy.

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Investments (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash
Cash	$ 6,068,579us-gaap_Cash	$ 7,887,502us-gaap_Cash
Cash equivalents
Money market funds	39,464,864us-gaap_MoneyMarketFundsAtCarryingValue	44,959,438us-gaap_MoneyMarketFundsAtCarryingValue
Cash and cash equivalents	45,533,443	52,846,940	33,996,866	61,352,483
Short-term investments (due within 1 year)
Total short-term investments	79,536,211us-gaap_ShortTermInvestments	70,434,148us-gaap_ShortTermInvestments
Long-term investments (due after 1 year through 2 years)
Total long-term investments	81,761,177us-gaap_LongTermInvestments	25,571,659us-gaap_LongTermInvestments
US Treasury Securities [Member]
Short-term investments (due within 1 year)
Total short-term investments		5,013,850
Long-term investments (due after 1 year through 2 years)
Total long-term investments	38,623,495
US Government Agencies Debt Securities [Member]
Short-term investments (due within 1 year)
Total short-term investments	38,928,806	33,609,886
Long-term investments (due after 1 year through 2 years)
Total long-term investments	35,203,355	14,821,065
Corporate Debt Securities [Member]
Short-term investments (due within 1 year)
Total short-term investments	40,607,405	31,810,412
Long-term investments (due after 1 year through 2 years)
Total long-term investments	7,934,327	10,750,594
Fair Value, Inputs, Level 1 [Member]
Cash
Cash	6,068,579	7,887,502
Cash equivalents
Money market funds	39,464,864	44,959,438
Cash and cash equivalents	45,533,443	52,846,940
Short-term investments (due within 1 year)
Total short-term investments	38,928,806	38,623,736
Long-term investments (due after 1 year through 2 years)
Total long-term investments	73,826,850	14,821,065
Fair Value, Inputs, Level 1 [Member] \| US Treasury Securities [Member]
Short-term investments (due within 1 year)
Total short-term investments		5,013,850
Long-term investments (due after 1 year through 2 years)
Total long-term investments	38,623,495
Fair Value, Inputs, Level 1 [Member] \| US Government Agencies Debt Securities [Member]
Short-term investments (due within 1 year)
Total short-term investments	38,928,806	33,609,886
Long-term investments (due after 1 year through 2 years)
Total long-term investments	35,203,355	14,821,065
Fair Value, Inputs, Level 1 [Member] \| Corporate Debt Securities [Member]
Short-term investments (due within 1 year)
Total short-term investments	0	0
Long-term investments (due after 1 year through 2 years)
Total long-term investments	0	0
Fair Value, Inputs, Level 2 [Member]
Cash
Cash	0	0
Cash equivalents
Money market funds	0	0
Cash and cash equivalents	0	0
Short-term investments (due within 1 year)
Total short-term investments	40,607,405	31,810,412
Long-term investments (due after 1 year through 2 years)
Total long-term investments	7,934,327	10,750,594
Fair Value, Inputs, Level 2 [Member] \| US Treasury Securities [Member]
Short-term investments (due within 1 year)
Total short-term investments		0
Long-term investments (due after 1 year through 2 years)
Total long-term investments	0
Fair Value, Inputs, Level 2 [Member] \| US Government Agencies Debt Securities [Member]
Short-term investments (due within 1 year)
Total short-term investments	0	0
Long-term investments (due after 1 year through 2 years)
Total long-term investments	0	0
Fair Value, Inputs, Level 2 [Member] \| Corporate Debt Securities [Member]
Short-term investments (due within 1 year)
Total short-term investments	40,607,405	31,810,412
Long-term investments (due after 1 year through 2 years)
Total long-term investments	7,934,327	10,750,594
Cost [Member]
Cash
Cash	6,068,579	7,887,502
Cash equivalents
Money market funds	39,464,864	44,959,438
Cash and cash equivalents	45,533,443	52,846,940
Short-term investments (due within 1 year)
Total short-term investments	79,593,720	70,396,681
Long-term investments (due after 1 year through 2 years)
Total long-term investments	81,797,004	25,551,349
Cost [Member] \| US Treasury Securities [Member]
Short-term investments (due within 1 year)
Total short-term investments		5,009,194
Long-term investments (due after 1 year through 2 years)
Total long-term investments	38,626,279
Cost [Member] \| US Government Agencies Debt Securities [Member]
Short-term investments (due within 1 year)
Total short-term investments	38,934,684	33,598,370
Long-term investments (due after 1 year through 2 years)
Total long-term investments	35,223,450	14,807,642
Cost [Member] \| Corporate Debt Securities [Member]
Short-term investments (due within 1 year)
Total short-term investments	40,659,036	31,789,117
Long-term investments (due after 1 year through 2 years)
Total long-term investments	$ 7,947,275	$ 10,743,707