Commitments and contingencies - Activity in the Repurchase Reserve (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Commitments and Contingencies [Roll Forward]
Balance at beginning of period	$ 5,928	$ 3,529	$ 3,273
Provision for loan repurchases or indemnifications	(766)	2,607	362
Losses on loans repurchased or indemnified	(360)	(208)	(106)
Balance at end of period	$ 4,802	$ 5,928	$ 3,529