Acquisitions (Condensed Balance Sheet of Carolina Bank and Asheville Savings Bank and Related Fair Value Adjustments) (Details) - USD ($) $ in Thousands							6 Months Ended
		Oct. 01, 2017		Mar. 03, 2017	Mar. 03, 2017		Jun. 30, 2017	Jun. 30, 2018	Dec. 31, 2017
Assets
Core deposit intangible		$ 9,880		$ 8,790	$ 8,790
Fair Value Adjustments
Value of stock issued							$ 114,478
Goodwill recorded related to acquisition							$ 139,124	$ 232,458	$ 233,070
Carolina Bank [Member]
Assets
Cash and cash equivalents				81,466	81,466
Securities				49,629	49,629
Loans, gross				505,560	505,560
Allowance for loan losses				(5,746)	(5,746)
Premises and equipment				17,967	17,967
Core deposit intangible
Other				34,976	34,976
Total				683,852	683,852
Liabilities
Deposits				584,950	584,950
Borrowings				21,855	21,855
Other				12,855	12,855
Total				619,660	619,660
Fair Value Adjustments
Value of stock issued				114,500
Cash paid in the acquisition				25,300
Goodwill recorded related to acquisition				65,072	65,072
As Recorded by First Bancorp [Member]
Assets
Cash and cash equivalents		41,824		81,464	81,464
Securities		95,020		49,368	49,368
Loans, gross		606,180		497,522	497,522
Allowance for loan losses
Presold mortgages		3,785
Premises and equipment		20,554		21,899	21,899
Core deposit intangible		9,880		8,790	8,790
Other		29,316		32,397	32,397
Total		806,559		691,440	691,440
Liabilities
Deposits		679,137		585,381	585,381
Borrowings		20,000		18,738	18,738
Other		8,419		12,636	12,636
Total		707,556		616,755	616,755
Net identifiable assets acquired		99,003		$ 74,685	74,685
Fair Value Adjustments [Member]
Fair Value Adjustments
Cash and cash equivalents					(2)	[1]
Securities					(261)	[2]
Loans, gross	[3]	(9,631)			(5,469)
Write-down of purchased credit impaired loans	[4]	(1,348)			(2,715)
Allowance for loan losses	[5]	6,685			5,746
Premises and equipment	[6]	9,857			4,251
Core deposit intangible		9,760	[7]		8,790	[8]
Other	[9]	(5,851)			(4,804)
Total Assets		9,472			5,536
Deposits		430	[10]		431	[11]
Borrowings					(2,855)	[12]
Other	[13]	298			225
Total Liabilities		728			(2,199)
Value of stock issued		169,299			114,478
Cash paid in the acquisition		17,939			25,279
Total cost of acquisition		187,238			139,757
Measurement Period Adjustments [Member]
Fair Value Adjustments
Cash and cash equivalents
Securities
Loans, gross					146	[14]
Write-down of purchased credit impaired loans
Allowance for loan losses
Premises and equipment					(319)	[15]
Core deposit intangible		120	[16]
Other		(777)	[17]		2,225	[18]
Total Assets		(657)			2,052
Deposits
Borrowings					(262)	[19]
Other		(822)	[20]		(444)	[21]
Total Liabilities		(822)			$ (706)
Asheville Savings Bank [Member]
Assets
Cash and cash equivalents		41,824
Securities		95,020
Loans, gross		617,159
Allowance for loan losses		(6,685)
Presold mortgages		3,785
Premises and equipment		10,697
Core deposit intangible
Other		35,944
Total		797,744
Liabilities
Deposits		678,707
Borrowings		20,000
Other		8,943
Total		707,650
Fair Value Adjustments
Value of stock issued		169,300
Cash paid in the acquisition		17,900
Goodwill recorded related to acquisition		$ 88,235

[1] This adjustment was recorded to a short-term investment to its estimated fair value.

[2] This fair value adjustment was recorded to adjust the securities portfolio to its estimated fair value.

[3] This fair value adjustment represents the amount necessary to reduce performing loans to their fair value due to interest rate factors and credit factors. Assuming the loans continue to perform, this amount will be amortized to increase interest income over the remaining lives of the related loans.

[4] This fair value adjustment was recorded to write-down purchased credit impaired loans assumed in the acquisition to their estimated fair market value.

[5] This fair value adjustment reduced the allowance for loan losses to zero as required by relevant accounting guidance.

[6] This adjustment represents the amount necessary to increase premises and equipment from its book value on the date of acquisition to its estimated fair market value.

[7] This fair value adjustment represents the value of the core deposit base assumed in the acquisition based on a study performed by an independent consulting firm. This amount was recorded by the Company as an identifiable intangible asset and is being amortized as expense on an accelerated basis over seven years.

[8] This fair value adjustment represents the value of the core deposit base assumed in the acquisition based on a study performed by an independent consulting firm. This amount was recorded by the Company as an identifiable intangible asset and will be amortized as expense on an accelerated basis over seven years.

[9] This fair value adjustment primarily represents the net deferred tax liability associated with the other fair value adjustments made to record the transaction.

[10] This fair value adjustment was recorded because the weighted average interest rate of Asheville Savings Bank's time deposits exceeded the cost of similar wholesale funding at the time of the acquisition. This amount is being amortized to reduce interest expense on an accelerated basis over their remaining five year life.

[11] This fair value adjustment was recorded because the weighted average interest rate of Carolina Bank's time deposits exceeded the cost of similar wholesale funding at the time of the acquisition. This amount is being amortized to reduce interest expense on an accelerated basis over their remaining five year life.

[12] This fair value adjustment was primarily recorded because the interest rate of Carolina Bank's trust preferred securities was less than the current interest rate on similar instruments. This amount is being amortized on approximately a straight-line basis to increase interest expense over the remaining life of the related borrowing, which is 18 years.

[13] This fair value adjustment represents miscellaneous adjustments needed to record assets and liabilities at their fair value.

[14] This fair value adjustment was a miscellaneous adjustment to increase the initial fair value of gross loans.

[15] This fair value adjustment relates to miscellaneous adjustment to decrease the initial fair value of premises and equipment.

[16] This fair value adjustment relates to a change in the final amount of the core deposit intangible asset from the amount originally estimated.

[17] This fair value adjustment relates to the write-down of a foreclosed property based on an updated appraisal and the related deferred tax asset adjustment.

[18] This fair value adjustment relates to changes in the estimate of deferred tax assets/liabilities associated with the acquisition and adjustments to decrease the initial fair value of the foreclosed real estate acquired in the transaction based on newly obtained valuations.

[19] This fair value adjustment relates to miscellaneous adjustments to decrease the initial fair value of borrowings.

[20] This fair value adjustment was recorded to adjust the tax liability assumed on the acquisition date based on updated information.

[21] This fair value adjustment relates to a change in the estimate of a contingent liability.