Fair value measurements (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Recurring
Certificate of deposit	$ 5,000,000
Marketable securities	8,586,090	8,570,338
Total Recurring	13,586,090	8,570,338
Nonrecurring
Investment in OC-BVI	6,930,384	6,925,346
Fair Value, Inputs, Level 1 [Member]
Recurring
Certificate of deposit	0
Marketable securities	8,586,090	8,570,338
Total Recurring	8,586,090	8,570,338
Nonrecurring
Investment in OC-BVI	0	0
Fair Value, Inputs, Level 2 [Member]
Recurring
Certificate of deposit	5,000,000
Marketable securities	0	0
Total Recurring	5,000,000	0
Nonrecurring
Investment in OC-BVI	0	0
Fair Value, Inputs, Level 3 [Member]
Recurring
Certificate of deposit	0
Marketable securities	0	0
Total Recurring	0	0
Nonrecurring
Investment in OC-BVI	$ 6,930,384	$ 6,925,346