Commitments and Loss Contingencies - Financial Instruments with Off-Balance Sheet Risk (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2020
Commitments and Contingencies
Commitments to extend credit, fixed rate	$ 124,609,000	$ 158,817,000
Commitments to extend credit, variable rate	989,584,000	961,821,000
Commitment to extend credit, total	$ 1,114,193,000	$ 1,120,638,000
Percentage of unused commitments to outstanding gross loans	42.00%	44.00%
Off-Balance Sheet, Credit Loss, Liability, Credit Loss Expenses (Reduction)	$ 192,000
Off-balance sheet credit exposures	1,078,000		$ 679,000
Off-balance sheet, credit loss liability increase due to offsetting increase in loss factors in CECL model	399,000
Restatement Adjustment | ASU 2016-03 - Topic 326
Commitments and Contingencies
Off-balance sheet credit exposures	(207,000)	$ (207,000)
Unused lines of credit and commitments to make loans
Commitments and Contingencies
Commitments to extend credit, fixed rate	121,560,000	147,372,000
Commitments to extend credit, variable rate	970,614,000	951,206,000
Commitment to extend credit, total	1,092,174,000	1,098,578,000
Standby letters of credit
Commitments and Contingencies
Commitments to extend credit, fixed rate	3,049,000	11,445,000
Commitments to extend credit, variable rate	18,970,000	10,615,000
Commitment to extend credit, total	$ 22,019,000	$ 22,060,000