Borrowings and Borrowings Availability - Narrative (Details) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Short-term borrowings		$ 253,000,000.0
Borrowings	$ 64,409,000	303,430,000
Trust Preferred Securities due January 2034
Debt Instrument [Line Items]
Borrowings	$ 20,600,000
Trust Preferred Securities due January 2034 \| Three-month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.70%
First Bancorp Capital Trust III
Debt Instrument [Line Items]
Borrowings	$ 10,300,000
Trust Preferred Securities due June 2036
Debt Instrument [Line Items]
Borrowings	$ 25,800,000
Trust Preferred Securities due June 2036 \| Three-month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.39%
Trust Preferred Securities due January 2035
Debt Instrument [Line Items]
Borrowings	$ 10,300,000
Trust Preferred Securities due January 2035 \| Three-month LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	2.00%
FHLB Line of Credit
Debt Instrument [Line Items]
Line of credit, borrowing capacity	$ 1,020,000,000.00
Line of credit, outstanding	8,000,000	247,000,000
Federal Funds Line of Credit
Debt Instrument [Line Items]
Line of credit, borrowing capacity	100,000,000
Line of credit, outstanding	0	0
FRB Line of Credit
Debt Instrument [Line Items]
Line of credit, outstanding	0	$ 0
Unused portion	$ 134,000,000

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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