Goodwill and Other Intangibles - Summary of Goodwill and Other Intangible Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Balances not subject to amortization
Goodwill	$ 372,472	$ 369,477
Balances subject to amortization
Total other intangible assets	7,300	7,057
Total goodwill and other intangible assets	379,772	376,534
Insurance agency
Balances subject to amortization
Balances subject to amortization	7,234	6,899
Core deposit intangible
Balances subject to amortization
Balances subject to amortization	66	158
Banking Business
Balances not subject to amortization
Goodwill	298,611	298,611
Balances subject to amortization
Total other intangible assets	66	158
Total goodwill and other intangible assets	298,677	298,769
Banking Business \| Insurance agency
Balances subject to amortization
Balances subject to amortization	0	0
Banking Business \| Core deposit intangible
Balances subject to amortization
Balances subject to amortization	66	158
Insurance Agency Business
Balances not subject to amortization
Goodwill	73,861	70,866
Balances subject to amortization
Total other intangible assets	7,234	6,899
Total goodwill and other intangible assets	81,095	77,765
Insurance Agency Business \| Insurance agency
Balances subject to amortization
Balances subject to amortization	7,234	6,899
Insurance Agency Business \| Core deposit intangible
Balances subject to amortization
Balances subject to amortization	$ 0	$ 0

Balances not subject to amortisation.

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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Carrying amount of finite-lived intangible assets, indefinite-lived intangible assets and goodwill. Goodwill is an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Intangible assets are assets, not including financial assets, lacking physical substance.

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Amount after accumulated amortization of finite-lived and indefinite-lived intangible assets classified as other.

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