Fair Value Measurement - Estimates Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financial Assets
Cash and due from banks	$ 905,447	$ 234,796
Equity securities	13,047	12,343
Available-for-sale debt securities	1,978,136	2,393,558
Held-to-maturity debt securities	731,212	851,753
Loans held for sale	168,378	43,013
Accrued interest receivable	66,790	43,648
Financial Liabilities
Deposits	12,429,373	11,004,006
Federal Home Loan Bank borrowings	549,003	1,415,615
Other borrowings	241,950	282,362
Subordinated debt and junior subordinated debt	192,291	199,869
Accrued interest payable	4,314	8,077
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Financial Assets
Cash and due from banks	905,447	234,796
Equity securities	13,047	12,343
Accrued interest receivable	66,790	43,648
Financial Liabilities
Deposits	10,810,863	8,948,086
Other borrowings	235,796	279,345
Accrued interest payable	4,314	8,077
Significant Other Observable Inputs (Level 2) [Member]
Financial Assets
Available-for-sale debt securities	1,976,601	2,391,953
Held-to-maturity debt securities	767,720	873,995
Loans held for sale	168,378	43,013
Other assets—interest rate derivatives	46,418	14,585
Financial Liabilities
Deposits	1,629,118	2,041,732
Federal Home Loan Bank borrowings	555,375	1,420,302
Other borrowings		3,346
Subordinated debt and junior subordinated debt	105,768	122,934
Other liabilities—interest rate derivatives	49,917	16,117
Significant Unobservable Inputs (Level 3) [Member]
Financial Assets
Available-for-sale debt securities	1,535	1,605
Held-to-maturity debt securities	463	528
Net loans	10,802,883	10,297,989
Financial Liabilities
Subordinated debt and junior subordinated debt	68,684	65,415
Carrying Amount [Member]
Financial Assets
Cash and due from banks	905,447	234,796
Equity securities	13,047	12,343
Available-for-sale debt securities	1,978,136	2,393,558
Held-to-maturity debt securities	730,886	851,753
Net loans	10,603,406	10,215,556
Loans held for sale	168,378	43,013
Other assets—interest rate derivatives	46,418	14,585
Accrued interest receivable	66,790	43,648
Financial Liabilities
Deposits	12,429,373	11,004,006
Federal Home Loan Bank borrowings	549,003	1,415,615
Other borrowings	241,950	282,362
Subordinated debt and junior subordinated debt	192,291	199,869
Other liabilities—interest rate derivatives	49,917	16,117
Accrued interest payable	4,314	8,077
Fair Value Estimate [Member]
Financial Assets
Cash and due from banks	905,447	234,796
Equity securities	13,047	12,343
Available-for-sale debt securities	1,978,136	2,393,558
Held-to-maturity debt securities	768,183	874,523
Net loans	10,802,883	10,297,989
Loans held for sale	168,378	43,013
Other assets—interest rate derivatives	46,418	14,585
Accrued interest receivable	66,790	43,648
Financial Liabilities
Deposits	12,439,981	10,989,818
Federal Home Loan Bank borrowings	555,375	1,420,302
Other borrowings	235,796	282,691
Subordinated debt and junior subordinated debt	174,452	188,349
Other liabilities—interest rate derivatives	49,917	16,117
Accrued interest payable	$ 4,314	$ 8,077