Federal funds purchased and securities sold under agreements to repurchase - Repurchase Agreements - Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	$ 42,197	$ 27,272
U.S. Treasury
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	0	754
U.S. government-sponsored enterprises
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	22,319	12,853
Mortgage-backed securities
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	19,878	13,665
Overnight and continuous
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	42,197	27,272
Overnight and continuous | U.S. Treasury
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	0	754
Overnight and continuous | U.S. government-sponsored enterprises
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	22,319	12,853
Overnight and continuous | Mortgage-backed securities
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	19,878	13,665
Less than 90 days
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	0	0
Less than 90 days | U.S. Treasury
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	0	0
Less than 90 days | U.S. government-sponsored enterprises
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	0	0
Less than 90 days | Mortgage-backed securities
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	0	0
Greater than 90 days
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	0	0
Greater than 90 days | U.S. Treasury
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	0	0
Greater than 90 days | U.S. government-sponsored enterprises
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	0	0
Greater than 90 days | Mortgage-backed securities
Federal funds purchased and securities sold under agreements to repurchase
Repurchase agreements	$ 0	$ 0