Goodwill and Other Intangible Assets, Summary of Core Deposit 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	Dec. 31, 2019
Summary of core deposit intangibles and other intangibles
Other intangible amortization	$ 2,203	$ 2,253	$ 6,642	$ 7,939
Core Deposit Intangibles
Summary of core deposit intangibles and other intangibles
Gross carrying amount at the beginning of period					$ 88,109	$ 80,730
Additions during the period			0		7,379
Accumulated amortization	(27,814)		(27,814)		(21,205)
Net book value	60,296		60,296		66,904
Other intangible amortization			6,608		8,749
Other Intangibles
Summary of core deposit intangibles and other intangibles
Gross carrying amount at the beginning of period					2,000	$ 38,970
Additions during the period			0		200
Accumulated amortization	(683)		(683)		(20,385)
Net book value	$ 0		0		1,350
Other intangible amortization			33		1,443
Other Intangibles | Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member]
Summary of core deposit intangibles and other intangibles
Reductions due to sale			$ (1,317)		$ (17,435)