Acquisitions - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Oct. 31, 2019	Apr. 12, 2019	Dec. 31, 2020	Dec. 31, 2019	Oct. 30, 2019	Apr. 11, 2019
Liabilities Assumed
Goodwill			$ 1,075,305	$ 1,055,520
Landrum Company
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
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	0				(22,736)
Foreclosed assets	190				373
Premises and equipment	82,659				63,878
Bank owned life insurance	19,206				19,206
Goodwill	0				407
Other assets	20,634				33,924
Total assets acquired	3,399,152				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	40,926				31,057
Total liabilities assumed	3,134,498				3,125,207
Total equity assumed	0				256,682
Total liabilities and equity assumed	3,134,498				3,381,889
Net assets acquired	264,654
Purchase price	415,779
Goodwill	151,125		131,300
Landrum Company | Core deposit intangible
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
Core deposit intangible	24,345				0
Landrum Company | Other intangibles
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
Core deposit intangible	5,116				$ 412
Landrum Company | Fair Value Adjustments
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
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	18,781
Bank owned life insurance	0
Goodwill	(407)
Other assets	(13,290)
Total assets acquired	17,263
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	9,869
Total liabilities assumed	9,291
Total equity assumed	(256,682)
Total liabilities and equity assumed	(247,391)
Landrum Company | Fair Value Adjustments | Core deposit intangible
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
Core deposit intangible	24,345
Landrum Company | Fair Value Adjustments | Other intangibles
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
Core deposit intangible	$ 4,704
Reliance Bancshares, Inc.
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
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
Total deposits		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
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
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)
Total deposits		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)