Acquisitions - Narrative (Details) $ / shares in Units, $ in Thousands		3 Months Ended			12 Months Ended
	Jan. 01, 2023 USD ($) option branchOffice $ / shares shares	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2023 USD ($)
Business Acquisition [Line Items]
Price per share, at acquisition date | $ / shares	$ 42.84
Goodwill		$ 478,750			$ 478,750
Financing receivable, excluding accrued interest, credit loss expense (reversal)		1,800	$ 11,451		19,750
Unfunded Loan Commitment
Business Acquisition [Line Items]
Financing receivable, excluding accrued interest, credit loss expense (reversal)		$ (601)		$ (870)	(3,858)
Core deposit intangibles
Business Acquisition [Line Items]
Useful life		10 years
GrandSouth
Business Acquisition [Line Items]
Common stock portion, number of First Bancorp's stock for each share of acquiree common stock converted (in shares) | shares	0.91
Number of shares issued | shares	5,032,834
Common stock options converted | option	542,345
Business acquisition, equity interest issued or issuable, common stock options, converted, exercise price (in dollars per share) | $ / shares	$ 20.14
Less: Total consideration	$ 229,489
Number of locations | branchOffice	8
Goodwill	$ 114,487
Fair value mark	29,500
Initial allowance recorded for PCD loans	$ 5,610
GrandSouth | Unfunded Loan Commitment
Business Acquisition [Line Items]
Financing receivable, excluding accrued interest, credit loss expense (reversal)		$ 0		$ 1,921	$ 1,921
GrandSouth | Core deposit intangibles
Business Acquisition [Line Items]
Useful life	10 years
Weighted average useful life	41 months