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Fair Value - Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Trading securities	$ 5,596	$ 5,584	$ 5,235
Investment securities available-for-sale	3,181,665	3,196,207	2,814,338
Derivative assets	14,993	14,118
Derivative liabilities	21,196	16,292
U.S. Treasury [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	5,257	5,551	5,634
U.S. Government-Sponsored Entities and Agencies [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	568,231	664,286	580,624
Mortgage-Backed Securities - Agency [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	1,448,526	1,667,682	1,462,111
States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	797,533	530,193	$ 431,874
Pooled Trust Preferred Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	8,205	8,448
Other Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	353,913	320,047
Estimate of Fair Value Measurement [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Trading securities	5,596	5,584
Estimate of Fair Value Measurement [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Residential loans held for sale	26,198	17,930
Derivative assets	14,993	14,118
Derivative liabilities	21,196	16,292
Estimate of Fair Value Measurement [Member] \| U.S. Treasury [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	5,257	5,551
Estimate of Fair Value Measurement [Member] \| U.S. Government-Sponsored Entities and Agencies [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	568,231	664,286
Estimate of Fair Value Measurement [Member] \| Mortgage-Backed Securities - Agency [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	1,448,526	1,667,682
Estimate of Fair Value Measurement [Member] \| States and Political Subdivisions [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	793,505	530,193
Estimate of Fair Value Measurement [Member] \| States and Political Subdivisions [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	4,028
Estimate of Fair Value Measurement [Member] \| Pooled Trust Preferred Securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	8,205	8,448
Estimate of Fair Value Measurement [Member] \| Other Securities [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	30,259	30,965
Estimate of Fair Value Measurement [Member] \| Other Securities [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	323,654	289,082
Carrying Value [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Trading securities	5,596	5,584
Residential loans held for sale	26,198	17,930
Derivative assets	14,993	14,118
Derivative liabilities	21,196	16,292
Carrying Value [Member] \| U.S. Treasury [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	5,257	5,551
Carrying Value [Member] \| U.S. Government-Sponsored Entities and Agencies [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	568,231	664,286
Carrying Value [Member] \| Mortgage-Backed Securities - Agency [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	1,448,526	1,667,682
Carrying Value [Member] \| States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	797,533	530,193
Carrying Value [Member] \| Pooled Trust Preferred Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	8,205	8,448
Carrying Value [Member] \| Other Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investment securities available-for-sale	$ 353,913	$ 320,047