Credit Quality - Schedule of Age Analysis of its Past Due Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	$ 66,619	$ 65,816
Loans, Total Past Due	205,593	186,906
Loans, Current & Other	17,826,961	13,526,642
Total Financing Receivables	18,032,554	13,713,548
Loans, Recorded Investment >90 Days & Accruing	11,150	9,494
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	138,974	121,090
Construction & Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	5,427	2,219
Loans, Total Past Due	12,315	18,262
Loans, Current & Other	1,763,413	1,389,943
Total Financing Receivables	1,775,728	1,408,205
Loans, Recorded Investment >90 Days & Accruing	84	0
Construction & Land Development [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	6,888	16,043
Commercial Real Estate [Member] \| Owner-Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	4,281	8,878
Loans, Total Past Due	37,480	20,087
Loans, Current & Other	1,587,280	1,181,565
Total Financing Receivables	1,624,760	1,201,652
Loans, Recorded Investment >90 Days & Accruing	1,419	544
Commercial Real Estate [Member] \| Owner-Occupied [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	33,199	11,209
Commercial Real Estate [Member] \| Nonowner-Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	3,633	6,318
Loans, Total Past Due	26,998	22,447
Loans, Current & Other	4,977,792	3,943,513
Total Financing Receivables	5,004,790	3,965,960
Loans, Recorded Investment >90 Days & Accruing	859	471
Commercial Real Estate [Member] \| Nonowner-Occupied [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	23,365	16,129
Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	10,781	5,238
Loans, Total Past Due	54,237	56,779
Loans, Current & Other	4,059,268	2,228,258
Total Financing Receivables	4,113,505	2,285,037
Loans, Recorded Investment >90 Days & Accruing	777	668
Other Commercial [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	43,456	51,541
Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	34,510	31,727
Loans, Total Past Due	64,393	56,070
Loans, Current & Other	4,245,763	3,630,331
Total Financing Receivables	4,310,156	3,686,401
Loans, Recorded Investment >90 Days & Accruing	6,234	6,256
Residential Real Estate [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	29,883	24,343
Consumer [Member] \| Bankcard [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	173	445
Loans, Total Past Due	333	663
Loans, Current & Other	8,132	9,411
Total Financing Receivables	8,465	10,074
Loans, Recorded Investment >90 Days & Accruing	160	218
Consumer [Member] \| Bankcard [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	160	218
Consumer [Member] \| Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	7,814	10,991
Loans, Total Past Due	9,837	12,598
Loans, Current & Other	1,185,313	1,143,621
Total Financing Receivables	1,195,150	1,156,219
Loans, Recorded Investment >90 Days & Accruing	1,617	1,337
Consumer [Member] \| Other Consumer [Member] \| Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	$ 2,023	$ 1,607

Financing receivables that are 30-89 days past due as of the balance sheet date.

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Amount of financing receivable 90 days or more past due and still accruing.

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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