Fair Value of Assets and Liabilities - Summary of Estimated Fair Values of Company Financial Instruments (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Financial Assets
Total available-for-sale securities	$ 737,227,000	$ 685,636,000
Held-to-maturity securities	10,162,000	69,572,000
Equity securities	185,000	412,000
Carrying Amount
Financial Assets
Cash and due from banks	231,087,000	84,154,000
Federal funds sold	1,298,000	926,000
Certificates of deposit investments	2,695,000	4,625,000
Total available-for-sale securities	737,227,000	685,636,000
Held-to-maturity securities	10,015,000	69,542,000
Equity securities	185,000	412,000
Loans held for sale	4,402,000	1,820,000
Loans net of allowance for loan losses	3,189,930,000	2,666,616,000
Interest receivable	20,228,000	15,577,000
Federal Reserve Bank stock	9,401,000	9,401,000
Federal Home Loan Bank stock	5,450,000	4,105,000
Financial Liabilities
Deposits	3,619,836,000	2,917,366,000
Securities sold under agreements to repurchase	170,345,000	208,109,000
Interest payable	1,838,000	2,261,000
Federal Home Loan Bank borrowings	93,954,000	113,895,000
Other borrowings		5,000,000
Junior subordinated debentures	18,985,000	18,858,000
Fair Value
Financial Assets
Cash and due from banks	231,087,000	84,154,000
Federal funds sold	1,298,000	926,000
Certificates of deposit investments	2,695,000	4,625,000
Total available-for-sale securities	737,227,000	685,636,000
Held-to-maturity securities	10,162,000	69,572,000
Equity securities	185,000	412,000
Loans held for sale	4,402,000	1,820,000
Loans net of allowance for loan losses	3,135,406,000	2,622,053,000
Interest receivable	20,228,000	15,577,000
Federal Reserve Bank stock	9,401,000	9,401,000
Federal Home Loan Bank stock	5,450,000	4,105,000
Financial Liabilities
Deposits	3,625,297,000	2,924,144,000
Securities sold under agreements to repurchase	170,349,000	208,016,000
Interest payable	1,838,000	2,261,000
Federal Home Loan Bank borrowings	97,174,000	114,510,000
Other borrowings		5,000,000
Junior subordinated debentures	14,235,000	15,596,000
Level 1
Financial Assets
Cash and due from banks	231,087,000	84,154,000
Federal funds sold	1,298,000	926,000
Certificates of deposit investments	0	0
Total available-for-sale securities	0	0
Held-to-maturity securities	0	0
Equity securities	185,000	219,000
Loans held for sale	0	0
Loans net of allowance for loan losses	0	0
Interest receivable	0	0
Federal Reserve Bank stock	0	0
Federal Home Loan Bank stock	0	0
Financial Liabilities
Deposits	0	0
Securities sold under agreements to repurchase	0	0
Interest payable	0	0
Federal Home Loan Bank borrowings	0	0
Other borrowings		5,000,000
Junior subordinated debentures	0	0
Level 2
Financial Assets
Cash and due from banks	0	0
Federal funds sold	0	0
Certificates of deposit investments	2,695,000	4,625,000
Total available-for-sale securities	736,434,000	684,856,000
Held-to-maturity securities	10,162,000	69,572,000
Equity securities	0	0
Loans held for sale	4,402,000	1,820,000
Loans net of allowance for loan losses	0	0
Interest receivable	20,228,000	15,577,000
Federal Reserve Bank stock	9,401,000	9,401,000
Federal Home Loan Bank stock	5,450,000	4,105,000
Financial Liabilities
Deposits	3,112,796,000	2,332,866,000
Securities sold under agreements to repurchase	170,349,000	208,016,000
Interest payable	1,838,000	2,261,000
Federal Home Loan Bank borrowings	97,174,000	114,510,000
Other borrowings		0
Junior subordinated debentures	14,285,000	15,596,000
Level 3
Financial Assets
Cash and due from banks	0	0
Federal funds sold	0	0
Certificates of deposit investments	0	0
Total available-for-sale securities	793,000	780,000
Held-to-maturity securities	0	0
Equity securities	0	193,000
Loans held for sale	0	0
Loans net of allowance for loan losses	3,135,406,000	2,622,053,000
Interest receivable	0	0
Federal Reserve Bank stock	0	0
Federal Home Loan Bank stock	0	0
Financial Liabilities
Deposits	512,501,000	591,278,000
Securities sold under agreements to repurchase	0	0
Interest payable	0	0
Federal Home Loan Bank borrowings	0	0
Other borrowings		0
Junior subordinated debentures	$ 0	$ 0