Fair value measurements - Fair value of assets and liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Carrying Value
Financial Assets
Cash and cash equivalents	$ 173,602	$ 238,214
Mortgage notes receivable, net	858,713	821,589
Interest and fees receivable	11,917	4,108
Investment in real property, net	3,743	5,837
Financial Liabilities
Accounts payable and accrued liabilities	3,504	8,415
Estimated Fair Value
Financial Assets
Cash and cash equivalents	173,602	238,214
Mortgage notes receivable, net	858,713	821,589
Interest and fees receivable	11,917	4,108
Investment in real property, net	3,743	5,837
Financial Liabilities
Accounts payable and accrued liabilities	3,504	8,415
Level 1 | Estimated Fair Value
Financial Assets
Cash and cash equivalents	173,602	238,214
Level 2 | Estimated Fair Value
Financial Assets
Interest and fees receivable	11,917	4,108
Financial Liabilities
Accounts payable and accrued liabilities	3,106	2,923
Level 3 | Estimated Fair Value
Financial Assets
Mortgage notes receivable, net	858,713	821,589
Investment in real property, net	3,743	5,837
Financial Liabilities
Accounts payable and accrued liabilities	$ 398	$ 5,492