Disclosures About Fair Value of Financial Instruments - Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	$ 3,543,180	$ 2,867,372
Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure	62,808	14,350
Interest-only GNMA securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	14,396	16,272
Equity securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	2,228
Derivative assets | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	65,127	23,608
Loans held for sale - fair value option | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	3,507	2,130
Loans held for sale - fair value option | Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure	17,600
Loans receivable, mortgage warehouse – fair value option | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	2,793,164	2,245,758
Derivative liabilities | Fair Value, Measurements, Recurring
Liabilities
Financial Liabilities Fair Value Disclosure	125,304	45,939
Impaired loans, net of specific reserves
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Related Allowance		852
Impaired loans, net of specific reserves | Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure	45,208	14,272
Other real estate owned | Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure		78
Available-for-sale Securities | Agency-guaranteed residential mortgage-backed securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	144,310	278,321
Available-for-sale Securities | Agency-guaranteed collateralized mortgage obligations | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	145,826
Available-for-sale Securities | State and political subdivision debt securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	18,389
Available-for-sale Securities | Corporate notes | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	356,233	298,877
Available-for-sale Securities | Equity securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure		2,406
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	2,228	2,406
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest-only GNMA securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	2,228
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivative assets | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Loans held for sale - fair value option | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Loans held for sale - fair value option | Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Loans receivable, mortgage warehouse – fair value option | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivative liabilities | Fair Value, Measurements, Recurring
Liabilities
Financial Liabilities Fair Value Disclosure	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Impaired loans, net of specific reserves | Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other real estate owned | Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Available-for-sale Securities | Agency-guaranteed residential mortgage-backed securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Available-for-sale Securities | Agency-guaranteed collateralized mortgage obligations | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Available-for-sale Securities | State and political subdivision debt securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Available-for-sale Securities | Corporate notes | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Available-for-sale Securities | Equity securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure		2,406
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	3,526,504	2,848,615
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure	17,600	0
Significant Other Observable Inputs (Level 2) | Interest-only GNMA securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0	0
Significant Other Observable Inputs (Level 2) | Equity securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0
Significant Other Observable Inputs (Level 2) | Derivative assets | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	65,075	23,529
Significant Other Observable Inputs (Level 2) | Loans held for sale - fair value option | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	3,507	2,130
Significant Other Observable Inputs (Level 2) | Loans held for sale - fair value option | Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure	17,600
Significant Other Observable Inputs (Level 2) | Loans receivable, mortgage warehouse – fair value option | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	2,793,164	2,245,758
Significant Other Observable Inputs (Level 2) | Derivative liabilities | Fair Value, Measurements, Recurring
Liabilities
Financial Liabilities Fair Value Disclosure	125,304	45,939
Significant Other Observable Inputs (Level 2) | Impaired loans, net of specific reserves | Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure	0	0
Significant Other Observable Inputs (Level 2) | Other real estate owned | Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure		0
Significant Other Observable Inputs (Level 2) | Available-for-sale Securities | Agency-guaranteed residential mortgage-backed securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	144,310	278,321
Significant Other Observable Inputs (Level 2) | Available-for-sale Securities | Agency-guaranteed collateralized mortgage obligations | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	145,826
Significant Other Observable Inputs (Level 2) | Available-for-sale Securities | State and political subdivision debt securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	18,389
Significant Other Observable Inputs (Level 2) | Available-for-sale Securities | Corporate notes | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	356,233	298,877
Significant Other Observable Inputs (Level 2) | Available-for-sale Securities | Equity securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure		0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	14,448	16,351
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure	45,208	14,350
Significant Unobservable Inputs (Level 3) | Interest-only GNMA securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	14,396	16,272
Significant Unobservable Inputs (Level 3) | Equity securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0
Significant Unobservable Inputs (Level 3) | Derivative assets | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	52	79
Significant Unobservable Inputs (Level 3) | Loans held for sale - fair value option | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0	0
Significant Unobservable Inputs (Level 3) | Loans held for sale - fair value option | Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure	0
Significant Unobservable Inputs (Level 3) | Loans receivable, mortgage warehouse – fair value option | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0	0
Significant Unobservable Inputs (Level 3) | Derivative liabilities | Fair Value, Measurements, Recurring
Liabilities
Financial Liabilities Fair Value Disclosure	0	0
Significant Unobservable Inputs (Level 3) | Impaired loans, net of specific reserves | Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure	45,208	14,272
Significant Unobservable Inputs (Level 3) | Other real estate owned | Fair Value, Measurements, Nonrecurring
Assets
Assets, Fair Value Disclosure		78
Significant Unobservable Inputs (Level 3) | Available-for-sale Securities | Agency-guaranteed residential mortgage-backed securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0	0
Significant Unobservable Inputs (Level 3) | Available-for-sale Securities | Agency-guaranteed collateralized mortgage obligations | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0
Significant Unobservable Inputs (Level 3) | Available-for-sale Securities | State and political subdivision debt securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	0
Significant Unobservable Inputs (Level 3) | Available-for-sale Securities | Corporate notes | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure	$ 0	0
Significant Unobservable Inputs (Level 3) | Available-for-sale Securities | Equity securities | Fair Value, Measurements, Recurring
Assets
Assets, Fair Value Disclosure		$ 0