Loans, net and allowance for loan losses - Schedule of Payment Deferrals Granted on Commercial Loans (Details) - Commercial - Loan Deferrals $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($) loan
Number of Loans | loan	479
Balance | $	$ 306,770
Percentage of Total Loan Portfolio	14.10%
Percentage of Tier 1 Capital (Bank)	113.70%
Lessors of Nonresidential Buildings
Number of Loans | loan	65
Balance | $	$ 71,899
Percentage of Total Loan Portfolio	3.30%
Percentage of Tier 1 Capital (Bank)	26.90%
Lessors of Residential Buildings and Dwellings
Number of Loans | loan	64
Balance | $	$ 53,564
Percentage of Total Loan Portfolio	2.50%
Percentage of Tier 1 Capital (Bank)	19.90%
Hotels and Motels
Number of Loans | loan	27
Balance | $	$ 39,261
Percentage of Total Loan Portfolio	1.80%
Percentage of Tier 1 Capital (Bank)	14.50%
Full-Service Restaurants
Number of Loans | loan	33
Balance | $	$ 27,783
Percentage of Total Loan Portfolio	1.30%
Percentage of Tier 1 Capital (Bank)	10.30%
Limited-Service Restaurants
Number of Loans | loan	8
Balance | $	$ 11,829
Percentage of Total Loan Portfolio	0.50%
Percentage of Tier 1 Capital (Bank)	4.40%
Gasoline Stations with Convenience Stores
Number of Loans | loan	18
Balance | $	$ 12,422
Percentage of Total Loan Portfolio	0.60%
Percentage of Tier 1 Capital (Bank)	4.60%
Construction and Mining
Number of Loans | loan	13
Balance | $	$ 9,718
Percentage of Total Loan Portfolio	0.40%
Percentage of Tier 1 Capital (Bank)	3.60%
Assisted Living Facilities for the Elderly
Number of Loans | loan	2
Balance | $	$ 6,319
Percentage of Total Loan Portfolio	0.30%
Percentage of Tier 1 Capital (Bank)	2.30%
Colleges, Universities, and Professional Schools
Number of Loans | loan	1
Balance | $	$ 6,301
Percentage of Total Loan Portfolio	0.30%
Percentage of Tier 1 Capital (Bank)	2.30%
All Others
Number of Loans | loan	248
Balance | $	$ 67,674
Percentage of Total Loan Portfolio	3.10%
Percentage of Tier 1 Capital (Bank)	24.90%