Goodwill and Other Intangible Assets - Changes in Goodwill and Other Intangibles (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Finite-lived Intangible Assets [Roll Forward]
Core deposit premiums, beginning of period	$ 111,110
Amortization of intangibles	(3,344)	$ (3,413)
Total	107,091		$ 111,110
Core deposit premiums, end of period	107,091		111,110
Core deposit intangible
Finite-lived Intangible Assets [Roll Forward]
Core deposit premiums, beginning of period	97,363	111,808	111,808
Disposition of intangible asset	(674)		(2,324)
Amortization of intangibles	(3,001)		(12,121)
Total	93,688	111,808	111,808
Core deposit premiums, end of period	93,688		97,363
Books of Business Intangible
Finite-lived Intangible Assets [Roll Forward]
Core deposit premiums, beginning of period	13,747	15,532	15,532
Disposition of intangible asset	0		(413)
Amortization of intangibles	(344)		(1,372)
Total	13,747	$ 15,532	13,747
Core deposit premiums, end of period	$ 13,403		$ 13,747