Fair Value - Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Equity securities, at fair value	$ 40,246	$ 6,842
Total investment securities - available-for-sale	5,447,271	5,385,091
Derivative assets	165,366	51,301
Derivative liabilities	22,425	12,393
U.S. Treasury
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	35,731	17,682
U.S. government-sponsored entities and agencies
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	453,501	592,984
Mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	3,304,054	3,183,861
States and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	1,355,959	1,275,643
Pooled trust preferred securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	7,185	8,222
Other securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	290,841	306,699
Fair Value on Recurring Basis | Carrying Value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Equity securities, at fair value	40,246	6,842
Residential loans held for sale	122,507	46,898
Derivative assets	165,366	51,301
Derivative liabilities	22,425	12,393
Fair Value on Recurring Basis | Carrying Value | U.S. Treasury
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	35,731	17,682
Fair Value on Recurring Basis | Carrying Value | U.S. government-sponsored entities and agencies
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	453,501	592,984
Fair Value on Recurring Basis | Carrying Value | Mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	3,304,054	3,183,861
Fair Value on Recurring Basis | Carrying Value | States and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	1,355,959	1,275,643
Fair Value on Recurring Basis | Carrying Value | Pooled trust preferred securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	7,185	8,222
Fair Value on Recurring Basis | Carrying Value | Other securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	290,841	306,699
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Equity securities, at fair value	40,246	6,842
Residential loans held for sale	0	0
Derivative assets	0	0
Derivative liabilities	0	0
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Equity securities, at fair value	0	0
Residential loans held for sale	122,507	46,898
Derivative assets	165,366	51,301
Derivative liabilities	22,425	12,393
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Equity securities, at fair value	0	0
Residential loans held for sale	0	0
Derivative assets	0	0
Derivative liabilities	0	0
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | U.S. Treasury | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	35,731	17,682
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | U.S. Treasury | Significant Other Observable Inputs (Level 2)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	0	0
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | U.S. Treasury | Significant Unobservable Inputs (Level 3)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	0	0
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | U.S. government-sponsored entities and agencies | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	0	0
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | U.S. government-sponsored entities and agencies | Significant Other Observable Inputs (Level 2)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	453,501	592,984
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | U.S. government-sponsored entities and agencies | Significant Unobservable Inputs (Level 3)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	0	0
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | Mortgage-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	0	0
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | Mortgage-backed securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	3,304,054	3,183,861
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | Mortgage-backed securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	0	0
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | States and political subdivisions | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	0	0
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | States and political subdivisions | Significant Other Observable Inputs (Level 2)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	1,355,959	1,275,603
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | States and political subdivisions | Significant Unobservable Inputs (Level 3)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	0	40
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | Pooled trust preferred securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	0	0
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | Pooled trust preferred securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	0	0
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | Pooled trust preferred securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	7,185	8,222
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | Other securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	0	31,169
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | Other securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	290,841	275,530
Fair Value on Recurring Basis | Estimate of Fair Value Measurement | Other securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total investment securities - available-for-sale	$ 0	$ 0