Goodwill and Other Intangible Assets - Changes in Goodwill and Other Intangibles (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Finite-lived Intangible Assets [Roll Forward]
Core deposit premiums, beginning of period			$ 111,110
Amortization of intangibles	$ (3,332)	$ (3,362)	(10,008)	$ (10,144)
Total	100,428		100,428		$ 111,110
Core deposit premiums, end of period	100,428		100,428		111,110
Core Deposit Premium
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			(8,978)		(12,121)
Total	87,711		87,711		97,363
Core deposit premiums, end of period	87,711		87,711		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			(1,030)		(1,372)
Total	12,717		12,717		13,747
Core deposit premiums, end of period	$ 12,717		$ 12,717		$ 13,747