Commitments and contingencies - Mortgage Loans (Details)	Sep. 30, 2018 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Within 1 year	$ 162,805
1 to 2 years	3,025,469
2 - 3 years	112,598
3 - 4 years	116,163
5 years and thereafter	3,707,158
Total	$ 7,124,193