Fair Value Measurements (Assets and Liabilities) (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	$ 1,918,473	$ 1,105,489
Equity securities	1,267	971
Derivative assets	76,919	109,114
Derivative Liability	78,212	117,597
Foreclosed assets	1,619	4,475
Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	99,522	1,009
Equity securities	1,267	971
Derivative assets	0	0
Derivative Liability	0	0
Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,818,951	1,104,480
Equity securities	0	0
Derivative assets	76,223	101,079
Derivative Liability	77,039	109,148
Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Equity securities	0	0
Derivative assets	0	0
Derivative Liability	0	0
Agency Obligations | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	1,009
Agency Obligations | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Agency Obligations | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,663,061	938,413
Mortgage-backed securities | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Mortgage-backed securities | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,663,061	938,413
Mortgage-backed securities | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	47,880	53,830
Asset-backed securities | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value
Asset-backed securities | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	47,880	53,830
Asset-backed securities | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value
State and municipal obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	69,484	71,258
State and municipal obligations | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
State and municipal obligations | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	69,484	71,258
State and municipal obligations | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Corporate obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	38,526	40,979
Corporate obligations | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Corporate obligations | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	38,526	40,979
Corporate obligations | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Measured on a Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,918,473	1,105,489
Equity securities	1,267	971
Derivative assets	76,223	101,079
Total assets acquired	1,995,963	1,207,539
Derivative Liability	77,039	109,148
Measured on a Recurring Basis | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	99,522	1,009
Equity securities	1,267	971
Derivative assets	0	0
Total assets acquired	100,789	1,980
Derivative Liability	0	0
Measured on a Recurring Basis | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,818,951	1,104,480
Equity securities	0	0
Derivative assets	76,223	101,079
Total assets acquired	1,895,174	1,205,559
Derivative Liability	77,039	109,148
Measured on a Recurring Basis | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Equity securities	0	0
Derivative assets	0	0
Total assets acquired	0	0
Derivative Liability	0	0
Measured on a Recurring Basis | U.S. Treasury obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	99,522
Measured on a Recurring Basis | U.S. Treasury obligations | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	99,522
Measured on a Recurring Basis | U.S. Treasury obligations | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0
Measured on a Recurring Basis | U.S. Treasury obligations | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0
Measured on a Recurring Basis | Agency Obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value		1,009
Measured on a Recurring Basis | Agency Obligations | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value		1,009
Measured on a Recurring Basis | Agency Obligations | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value		0
Measured on a Recurring Basis | Agency Obligations | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value		0
Measured on a Recurring Basis | Mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,663,061	938,413
Measured on a Recurring Basis | Mortgage-backed securities | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Measured on a Recurring Basis | Mortgage-backed securities | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	1,663,061	938,413
Measured on a Recurring Basis | Mortgage-backed securities | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Measured on a Recurring Basis | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	47,880	53,830
Measured on a Recurring Basis | Asset-backed securities | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Measured on a Recurring Basis | Asset-backed securities | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	47,880	53,830
Measured on a Recurring Basis | Asset-backed securities | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Measured on a Recurring Basis | State and municipal obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	69,484	71,258
Measured on a Recurring Basis | State and municipal obligations | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Measured on a Recurring Basis | State and municipal obligations | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	69,484	71,258
Measured on a Recurring Basis | State and municipal obligations | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Measured on a Recurring Basis | Corporate obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	38,526	40,979
Measured on a Recurring Basis | Corporate obligations | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Measured on a Recurring Basis | Corporate obligations | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	38,526	40,979
Measured on a Recurring Basis | Corporate obligations | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities, at fair value	0	0
Measured on a Non-Recurring Basis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets acquired	33,366	30,725
Loans measured for impairment based on the fair value of the underlying collateral	31,747	26,250
Foreclosed assets	1,619	4,475
Measured on a Non-Recurring Basis | Quoted Prices in Active  Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets acquired	0	0
Loans measured for impairment based on the fair value of the underlying collateral	0	0
Foreclosed assets	0	0
Measured on a Non-Recurring Basis | Significant Other Observable  Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets acquired	0	0
Loans measured for impairment based on the fair value of the underlying collateral	0	0
Foreclosed assets	0	0
Measured on a Non-Recurring Basis | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets acquired	33,366	30,725
Loans measured for impairment based on the fair value of the underlying collateral	31,747	26,250
Foreclosed assets	$ 1,619	$ 4,475