Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Allowance for loan losses	$ 14,097,000	$ 13,966,000
Loans	18,655,000	15,062,000
Deferred compensation	10,001,000	7,093,000
Net unrealized losses on securities	6,180,000	3,659,000
Impairment of assets	1,280,000	1,748,000
Net operating loss carryforwards	19,065,000	2,419,000
Other	3,610,000	4,722,000
Gross deferred tax assets	72,888,000	48,669,000
Valuation allowance on state net operating loss carryforwards	0	0
Total deferred tax assets	72,888,000	48,669,000
Deferred tax liabilities
Investment in partnerships	1,572,000	757,000
Depreciation	3,865,000	3,163,000
Mortgage servicing rights	12,350,000	10,139,000
Subordinated debt	1,607,000	2,394,000
Other	1,792,000	1,859,000
Total deferred tax liabilities	21,186,000	18,312,000
Net deferred tax assets	$ 51,702,000	$ 30,357,000