Mergers and Acquisitions - Acquisition date fair value of purchased assets and liabilities (Details) - USD ($) $ in Thousands	Feb. 01, 2018	Nov. 01, 2017	Jul. 31, 2017	Jul. 01, 2016	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Accrued interest receivable					$ 35,413		$ 32,459
Net deferred tax asset					2,640
Liabilities
Total identifiable net assets					130,000		115,000	$ 11,200
Consideration transferred
Goodwill					$ 307,112		$ 220,591	$ 142,025
NLFC Holdings Corp
Assets
Cash and cash equivalents	$ 27,700
Loans, net	358,352
Premises and equipment, net	324
Net deferred tax asset	2,873
Other assets	4,051
Total assets acquired	393,300
Liabilities
Short-term borrowings	214,923
Long-term debt	119,402
Other liabilities	16,108
Total liabilities assumed	350,433
Total identifiable net assets	42,867
Consideration transferred
Cash	84,500
Common stock issued	$ 45,746
Common stock issued (in shares)	1,443,987
Total fair value of consideration transferred	$ 130,246
Goodwill	87,379
NLFC Holdings Corp | As Recorded by NLFC | NLFC Holdings Corp
Assets
Cash and cash equivalents	27,700
Loans, net	365,533
Premises and equipment, net	628
Net deferred tax asset	0
Other assets	5,117
Total assets acquired	398,978
Liabilities
Short-term borrowings	214,923
Long-term debt	119,402
Other liabilities	17,059
Total liabilities assumed	351,384
Excess of assets acquired over liabilities assumed	47,594
NLFC Holdings Corp | Fair Value Adjustments
Assets
Cash and cash equivalents	0
Loans, net	(7,181)
Premises and equipment, net	(304)
Net deferred tax asset	2,873
Other assets	(1,066)
Total assets acquired	(5,678)
Liabilities
Short-term borrowings	0
Long-term debt	0
Other liabilities	(951)
Total liabilities assumed	(951)
Aggregate fair value adjustments	$ (4,727)
Four Oaks FinCorp, Inc
Assets
Cash and cash equivalents		$ 48,658
Securities		114,972
Loans held for sale		10,686				$ 10,700
Loans, net		486,244
Premises and equipment, net		12,398
Bank owned life insurance		20,339
Accrued interest receivable		1,740
Net deferred tax asset		17,334
Intangibles		8,738
Other real estate owned		659
Other assets		8,723
Total assets acquired		730,491
Liabilities
Deposits		565,205
Federal Home Loan Bank advances		65,224
Long-term debt		19,747
Other liabilities		7,390
Total liabilities assumed		657,566
Total identifiable net assets		72,925
Consideration transferred
Cash		12,802
Common stock issued		$ 113,665
Common stock issued (in shares)		4,145,343
Total fair value of consideration transferred		$ 126,467
Goodwill		53,542
Four Oaks FinCorp, Inc | As Recorded by FOFN | Four Oaks Bank
Assets
Cash and cash equivalents		48,652
Securities		114,190
Loans held for sale		13,976
Loans, net		491,721
Premises and equipment, net		11,251
Bank owned life insurance		20,339
Accrued interest receivable		1,858
Net deferred tax asset		18,333
Intangibles		0
Other real estate owned		1,173
Other assets		8,792
Total assets acquired		730,285
Liabilities
Deposits		563,840
Federal Home Loan Bank advances		65,000
Long-term debt		23,872
Other liabilities		7,330
Total liabilities assumed		660,042
Excess of assets acquired over liabilities assumed		70,243
Four Oaks FinCorp, Inc | Fair Value Adjustments
Assets
Cash and cash equivalents		6
Securities		782
Loans held for sale		(3,290)
Loans, net		(5,477)
Premises and equipment, net		1,147
Bank owned life insurance		0
Accrued interest receivable		(118)
Net deferred tax asset		(999)
Intangibles		8,738
Other real estate owned		(514)
Other assets		(69)
Total assets acquired		206
Liabilities
Deposits		1,365
Federal Home Loan Bank advances		224
Long-term debt		(4,125)
Other liabilities		60
Total liabilities assumed		(2,476)
Aggregate fair value adjustments		$ 2,682
HCSB Financial Corporation
Assets
Cash and cash equivalents			$ 17,853
Securities			101,320
Loans, net			215,947
Premises and equipment, net			7,424
Bank owned life insurance			11,827
Accrued interest receivable			1,047
Net deferred tax asset			25,579
Intangibles			5,716
Other real estate owned			805
Other assets			1,918
Total assets acquired			389,436
Liabilities
Deposits			318,942
Repurchase agreements			1,141
Federal Home Loan Bank advances			24,517
Other liabilities			2,046
Total liabilities assumed			346,646
Total identifiable net assets			42,790
Consideration transferred
Cash			31
Common stock issued			$ 65,800
Common stock issued (in shares)			2,370,331
Total fair value of consideration transferred			$ 65,831
Equity interest held before the business combination			1,125
Goodwill			24,166
HCSB Financial Corporation | As Recorded by HCSB | Horry County State Bank
Assets
Cash and cash equivalents			17,855
Securities			101,462
Loans, net			228,483
Premises and equipment, net			14,030
Bank owned life insurance			11,827
Accrued interest receivable			1,322
Net deferred tax asset			0
Intangibles			0
Other real estate owned			1,177
Other assets			1,950
Total assets acquired			378,106
Liabilities
Deposits			318,512
Repurchase agreements			1,141
Federal Home Loan Bank advances			24,000
Other liabilities			1,955
Total liabilities assumed			345,608
Excess of assets acquired over liabilities assumed			32,498
HCSB Financial Corporation | Fair Value Adjustments
Assets
Cash and cash equivalents			(2)
Securities			(142)
Loans, net			(12,536)
Premises and equipment, net			(6,606)
Bank owned life insurance			0
Accrued interest receivable			(275)
Net deferred tax asset			25,579
Intangibles			5,716
Other real estate owned			(372)
Other assets			(32)
Total assets acquired			11,330
Liabilities
Deposits			430
Repurchase agreements			0
Federal Home Loan Bank advances			517
Other liabilities			91
Total liabilities assumed			1,038
Aggregate fair value adjustments			$ 10,292
Tidelands Bancshares, Inc
Assets
Cash and cash equivalents				$ 13,121
Securities				65,521
Loans held for sale				142
Loans, net				305,903
Premises and equipment, net				11,189
Bank owned life insurance				16,917
Accrued interest receivable				919
Net deferred tax asset				15,712
Intangibles				1,570
Other real estate owned				7,495
Other assets				1,756
Total assets acquired				440,245
Liabilities
Deposits				399,873
Repurchase agreements				10,155
Federal Home Loan Bank advances				13,354
Long-term debt				10,766
Other liabilities				5,601
Total liabilities assumed				439,749
Total identifiable net assets				496
Consideration transferred
Total fair value of consideration transferred				11,209
Cash paid to redeem common stock				2,224
Cash paid to redeem preferred stock issued under the Treasury's Capital Purchase Program				8,985
Goodwill				10,713
Tidelands Bancshares, Inc | As Recorded by Tidelands | Tidelands Bank
Assets
Cash and cash equivalents				13,121
Securities				65,676
Loans held for sale				139
Loans, net				317,938
Premises and equipment, net				19,133
Bank owned life insurance				16,917
Accrued interest receivable				1,086
Net deferred tax asset				73
Intangibles				0
Other real estate owned				9,881
Other assets				1,920
Total assets acquired				445,884
Liabilities
Deposits				398,108
Repurchase agreements				10,000
Federal Home Loan Bank advances				13,000
Long-term debt				14,434
Other liabilities				11,587
Total liabilities assumed				447,129
Excess of assets acquired over liabilities assumed				(1,245)
Tidelands Bancshares, Inc | Fair Value Adjustments
Assets
Cash and cash equivalents				0
Securities				(155)
Loans held for sale				3
Loans, net				(12,035)
Premises and equipment, net				(7,944)
Bank owned life insurance				0
Accrued interest receivable				(167)
Net deferred tax asset				15,639
Intangibles				1,570
Other real estate owned				(2,386)
Other assets				(164)
Total assets acquired				(5,639)
Liabilities
Deposits				1,765
Repurchase agreements				155
Federal Home Loan Bank advances				354
Long-term debt				(3,668)
Other liabilities				(5,986)
Total liabilities assumed				(7,380)
Aggregate fair value adjustments				$ 1,741