Investments - Short term invesmtments (Details) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Notes to Financial Statements
U.S. treasury money market fund	$ 203,351	$ 3,494,729
Short-term U.S. treasury bills	92,282,830	78,776,954
Bank money market accounts	2,132,544	3,982,804
Bank savings accounts	1,792	1,762
Total short-term investments	$ 94,620,487	$ 86,256,249

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.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph g

-Article 7

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant