Cash and cash equivalents (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Line Items]
Bank accounts	$ 21,918,298	$ 29,094,936
Short term deposits	9,419,179	16,388,030
Total cash and cash equivalents	31,337,477	45,482,966	$ 37,554,116
United States dollar [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	11,797,054	6,764,201
Short term deposits	8,379,723	10,559,407
Cayman Islands dollar [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	5,626,487	4,306,768
Short term deposits	0	4,802,060
Bahamian dollar [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	3,301,002	13,310,936
Short term deposits	1,039,456	1,026,563
Belize dollar [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	1,130,783	4,646,184
Bermudian dollar [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	3,370	3,502
Mexican peso [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	37,313	17,014
Indonesian rupiah [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	$ 22,289	$ 46,331