Fair value measurement - Gains and losses (realized and unrealized) included in earnings for level 3 assets and liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Abstract
Gains (Losses) included in earnings	$ (6,260)	$ (7,646)	$ (5,757)	$ (12,886)
Changes in unrealized gains (losses) included in earnings relating to assets still held	(2,031)	(4,946)	3,135	(7,377)
Mortgage banking activities
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Abstract
Gains (Losses) included in earnings	(6,249)	(7,640)	(5,737)	(12,869)
Changes in unrealized gains (losses) included in earnings relating to assets still held	(2,036)	(4,947)	3,126	(7,386)
Trading gains losses
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Abstract
Gains (Losses) included in earnings	(11)	(6)	(20)	(17)
Changes in unrealized gains (losses) included in earnings relating to assets still held	$ 5	$ 1	$ 9	$ 9