Income Taxes - Significant components of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets
Allowance for credit losses	$ 28,118	$ 19,144
Deferred loan fees and costs	8,104	6,354
Leases	7,183	7,790
Stock-based compensation	828	674
Net operating loss	6,896	6,184
Unrealized loss on interest rate swap derivatives	132	53
SERP	2,495	1,541
Premises and equipment	879	914
Other assets	1,982	816
Valuation allowances	(5,845)	(4,899)
Total deferred tax assets	50,772	38,571
Deferred tax liabilities
Unrealized net gain on securities available-for-sale	(5,519)	(1,081)
Excess servicing	(206)	(51)
Intangible assets	0	(9)
Leases	(6,470)	(7,117)
Other liabilities	(6)	(509)
Total deferred tax liabilities	(12,201)	(8,767)
Net deferred income tax assets	$ 38,571	$ 29,804