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
	Mar. 31, 2020	Mar. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Abstract
Gains (Losses) included in earnings	$ (5,240)	$ (3,832)
Change in unrealized gain loss - Fair value assets	(2,432)	(744)
Mortgage banking activities
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Abstract
Gains (Losses) included in earnings	(5,229)	(3,825)
Change in unrealized gain loss - Fair value assets	(2,439)	(747)
Trading gains losses
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Abstract
Gains (Losses) included in earnings	(11)	(7)
Change in unrealized gain loss - Fair value assets	$ 7	$ 3