Cash and cash equivalents (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Line Items]
Bank accounts	$ 37,754,409	$ 27,871,149
Short term deposits	1,499,707	16,921,585
Total cash and cash equivalents	39,254,116	44,792,734	$ 35,713,689	$ 33,626,516
United States dollar [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	11,355,704	10,961,159
Short term deposits	490,914	1,307,337
Cayman Islands dollar [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	16,511,673	10,590,207
Bahamian dollar [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	4,859,914	1,983,236
Short term deposits	1,008,793	15,614,248
Belize dollar [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	4,884,161	4,213,923
Bermudian dollar [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	3,733	4,571
Mexican peso [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	72,507	27,872
Euro [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	11,657	23,819
Singapore dollar [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	25,840	25,879
Indonesian rupiah [Member]
Cash and Cash Equivalents [Line Items]
Bank accounts	$ 29,220	$ 40,483