Acquisitions - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Oct. 31, 2019	Apr. 12, 2019	Mar. 31, 2020	Dec. 31, 2019	Oct. 30, 2019	Apr. 11, 2019
Liabilities Assumed
Goodwill			$ 1,064,978	$ 1,055,520
Landrum Company
Assets Acquired
Cash and due from banks	$ 215,285				$ 215,285
Due from banks - time	248				248
Investment securities	1,025,983				1,021,755
Loans acquired	2,005,486				2,049,137
Allowance for loan losses					(22,736)
Foreclosed assets	190				373
Premises and equipment	82,745				63,878
Bank owned life insurance	19,206				19,206
Other assets	20,523				33,924
Total assets acquired	3,399,127				3,381,889
Liabilities Assumed
Non-interest bearing transaction accounts	716,675				716,675
Interest bearing transaction accounts and savings deposits	1,465,429				1,465,429
Time deposits	867,496				867,197
Total deposits	3,049,600				3,049,301
Other borrowings	10,055				10,055
Subordinated debentures	33,917				34,794
Accrued interest and other liabilities	30,573				31,057
Total liabilities assumed	3,124,145				3,125,207
Total equity assumed					256,682
Total liabilities and equity assumed	3,124,145				3,381,889
Net assets acquired	274,982
Purchase price	415,779
Goodwill	140,797			131,300	407
Landrum Company | Fair Value Adjustments
Assets Acquired
Cash and due from banks	0
Due from banks - time	0
Investment securities	4,228
Loans acquired	(43,651)
Allowance for loan losses	22,736
Foreclosed assets	(183)
Premises and equipment	18,867
Bank owned life insurance	0
Other assets	(13,401)
Total assets acquired	17,238
Liabilities Assumed
Non-interest bearing transaction accounts	0
Interest bearing transaction accounts and savings deposits	0
Time deposits	299
Total deposits	299
Other borrowings	0
Subordinated debentures	(877)
Accrued interest and other liabilities	(484)
Total liabilities assumed	(1,062)
Total equity assumed	(256,682)
Total liabilities and equity assumed	(257,744)
Goodwill	(407)
Reliance Bancshares, Inc.
Assets Acquired
Cash and due from banks		$ 25,693				$ 25,693
Due from banks - time		502				502
Investment securities		286,110				287,983
Loans acquired		1,096,870				1,138,527
Allowance for loan losses		0				(10,808)
Foreclosed assets		5,912				11,092
Premises and equipment		29,451				32,452
Bank owned life insurance		39,348				39,348
Core deposit intangible		18,350				0
Other assets		32,076				25,165
Total assets acquired		1,534,312				1,549,954
Liabilities Assumed
Non-interest bearing transaction accounts		108,812				108,845
Interest bearing transaction accounts and savings deposits		639,798				639,798
Time deposits		476,657				478,415
Total deposits		1,225,267				1,227,058
Securities sold under agreement to repurchase		14,146				14,146
Other borrowings		157,400				162,900
Accrued interest and other liabilities		8,453				8,185
Total liabilities assumed		1,405,266				1,412,289
Total equity assumed		0				137,665
Total liabilities and equity assumed		1,405,266				$ 1,549,954
Net assets acquired		129,046
Purchase price		207,539
Goodwill		78,493		$ 78,500
Reliance Bancshares, Inc. | Fair Value Adjustments
Assets Acquired
Cash and due from banks		0
Due from banks - time		0
Investment securities		(1,873)
Loans acquired		(41,657)
Allowance for loan losses		10,808
Foreclosed assets		(5,180)
Premises and equipment		(3,001)
Bank owned life insurance		0
Core deposit intangible		18,350
Other assets		6,911
Total assets acquired		(15,642)
Liabilities Assumed
Non-interest bearing transaction accounts		(33)
Interest bearing transaction accounts and savings deposits		0
Time deposits		(1,758)
Total deposits		(1,791)
Securities sold under agreement to repurchase		0
Other borrowings		(5,500)
Accrued interest and other liabilities		268
Total liabilities assumed		(7,023)
Total equity assumed		(137,665)
Total liabilities and equity assumed		$ (144,688)
Core deposit intangible | Landrum Company
Assets Acquired
Core deposit intangible	24,345				0
Core deposit intangible | Landrum Company | Fair Value Adjustments
Assets Acquired
Core deposit intangible	24,345
Other intangibles | Landrum Company
Assets Acquired
Core deposit intangible	5,116				$ 412
Other intangibles | Landrum Company | Fair Value Adjustments
Assets Acquired
Core deposit intangible	$ 4,704