Fair value measurements (Details) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Recurring
Cash equivalents	$ 7,579,819	$ 16,177,462
Restricted cash	0	7,500,000
Marketable securities	8,548,469	8,496,372
Total Recurring	16,128,288	32,173,834
Nonrecurring
Investment in affiliate	6,342,459	6,634,598
Fair Value, Inputs, Level 1 [Member]
Recurring
Total Recurring	16,128,288	32,173,834
Fair Value, Inputs, Level 2 [Member]
Recurring
Total Recurring	0	0
Fair Value, Inputs, Level 3 [Member]
Recurring
Total Recurring	0	0
Nonrecurring
Investment in affiliate	6,342,459	6,634,598
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Recurring
Cash equivalents	7,579,819	16,177,462
Marketable securities	8,548,469	8,496,372
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Recurring
Cash equivalents	0	0
Marketable securities	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Recurring
Cash equivalents	0	0
Marketable securities	0	0
Fair Value, Measurements, Nonrecurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Nonrecurring
Investment in affiliate	0	0
Fair Value, Measurements, Nonrecurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Nonrecurring
Investment in affiliate	$ 6,342,459	$ 6,634,598

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means 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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The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. For a classified balance sheet represents the current portion only (the noncurrent portion has a separate concept); there is a separate and distinct element for unclassified presentations.

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