Goodwill and Other Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Oct. 31, 2019	Apr. 12, 2019
Goodwill [Line Items]
Goodwill	$ 1,075,305	$ 1,055,520
Amortization of intangibles	$ 13,495	11,805	$ 11,009
Minimum
Goodwill [Line Items]
Finite-lived intangible asset, useful life	10 years
Maximum
Goodwill [Line Items]
Finite-lived intangible asset, useful life	15 years
Core deposit intangible
Goodwill [Line Items]
Amortization of intangibles	$ 12,121	10,694	9,500
Core deposit intangible | Minimum
Goodwill [Line Items]
Finite-lived intangible asset, useful life	10 years
Core deposit intangible | Maximum
Goodwill [Line Items]
Finite-lived intangible asset, useful life	15 years
Books of Business Intangible
Goodwill [Line Items]
Amortization of intangibles	$ 1,372	$ 1,111	$ 1,400
Landrum Company
Goodwill [Line Items]
Goodwill	131,300			$ 151,125
Goodwill increase	19,800
Reliance Bancshares, Inc.
Goodwill [Line Items]
Goodwill	$ 78,500				$ 78,493