Income Taxes - Significant Components of The Company's Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Deferred tax assets
Allowance for credit losses	$ 45,891	$ 14,304
Loans	11,579	10,284
Deferred compensation	11,605	12,050
Impairment of assets	1,631	1,108
Net operating loss carryforwards	2,607	9,387
Lease liabilities under operating leases	22,271	22,686
Other	208	934
Total deferred tax assets	95,792	70,753
Deferred tax liabilities
Net unrealized gains on securities	6,057	190
Investment in partnerships	982	967
Fixed assets	7,688	2,952
Mortgage servicing rights	14,121	13,472
Junior subordinated debt	2,237	2,304
Lease right-of-use asset	21,203	21,727
Other	1,457	1,859
Total deferred tax liabilities	53,745	43,471
Net deferred tax assets	$ 42,047	$ 27,282