Loans and Allowance for Loan Losses - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) property loan	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) loan property category	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Financing Receivable, Impaired [Line Items]
Foreclosed properties held	$ 4,300,000		$ 4,300,000
Investment in loans in the process of foreclosure	500,000		500,000
Investment in loans in the process of foreclosure, related allowance	0		$ 0
Number of points in internal risk rating system | category			9
Number of categories in internal risk rating system considered as not criticized | category			6
Commercial relationship credit review threshold amount	$ 1,000,000.0		$ 1,000,000.0
Past due period before loans placed in non-accrual status			90 days
Recent loan payment history before removal from non-accrual status			6 months
Allowance for loan losses, number of evaluation components | loan	2		2
Impaired loans collectively evaluated	$ 1,300,000		$ 1,300,000		$ 2,000,000.0
Impaired loans, related reserves	100,000		$ 100,000		100,000
Number of rolling quarters | loan			12
Liability for unfunded commitments	600,000		$ 600,000		$ 600,000
Increase (decrease) in allowance for credit loss	(100,000)	$ 200,000	(100,000)	$ 200,000
Collectively evaluated for impairment	1,659,711,000	1,430,770,000	1,659,711,000	1,430,770,000
Purchased credit impaired loans
Financing Receivable, Impaired [Line Items]
Collectively evaluated for impairment	23,100,000		23,100,000
Residential real estate
Financing Receivable, Impaired [Line Items]
Foreclosed properties held	$ 3,200,000		$ 3,200,000
Increase (decrease) in impaired loans (as a percentage)			74.40%
Number foreclosed properties held | property	16		16
Collectively evaluated for impairment	$ 248,969,000	276,544,000	$ 248,969,000	276,544,000
Residential real estate | Purchased credit impaired loans
Financing Receivable, Impaired [Line Items]
Collectively evaluated for impairment	8,900,000		8,900,000
Residential real estate | Other Loan Relationships
Financing Receivable, Impaired [Line Items]
Foreclosed properties held	$ 1,100,000		$ 1,100,000
Increase (decrease) in impaired loans (as a percentage)			25.60%
Commercial and non-residential real estate
Financing Receivable, Impaired [Line Items]
Number foreclosed properties held | property	14		14
Collectively evaluated for impairment	$ 1,375,895,000	1,113,420,000	$ 1,375,895,000	1,113,420,000
Commercial and non-residential real estate | Purchased credit impaired loans
Financing Receivable, Impaired [Line Items]
Collectively evaluated for impairment	13,900,000		$ 13,900,000
Consumer
Financing Receivable, Impaired [Line Items]
Number of additional collateralized loans in the process of foreclosure | loan			6
Investment in loans in the process of foreclosure	200,000		$ 200,000
Collectively evaluated for impairment	10,109,000	$ 3,525,000	10,109,000	$ 3,525,000
Consumer | Purchased credit impaired loans
Financing Receivable, Impaired [Line Items]
Collectively evaluated for impairment	400,000		400,000
The First State Bank | Consumer
Financing Receivable, Impaired [Line Items]
Investment in loans in the process of foreclosure	$ 300,000		$ 300,000