Fair Value Accounting - Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Repossessed Assets	$ 10,600	$ 13,900
Financial assets
Investment securities - HTM, at amortized cost; fair value of $530,062 at March 31, 2020 and $516,261 at December 31, 2019	483,775	485,107
Investment securities - AFS, at fair value; amortized cost of $3,640,109 at March 31, 2020 and $3,317,928 at December 31, 2019	3,676,651	3,346,310
Investment securities - equity	131,158	138,701
Loans, net	22,909,939	20,933,696
Accrued Investment Income Receivable	1,700
Financial liabilities
Deposits	24,830,681	22,796,493
Customer repurchase agreements	22,980	16,675
Junior subordinated debt	52,990	61,685
Fair Value, Nonrecurring [Member] | Reported Value Measurement [Member]
Financial assets
Investment securities - HTM, at amortized cost; fair value of $530,062 at March 31, 2020 and $516,261 at December 31, 2019	483,775	485,107
Loans, net	22,930,812	20,955,499
Financial liabilities
Deposits	24,830,681	22,796,493
Junior subordinated debt	389,893	393,563
Fair Value, Nonrecurring [Member] | Estimate of Fair Value Measurement [Member]
Financial assets
Investment securities - HTM, at amortized cost; fair value of $530,062 at March 31, 2020 and $516,261 at December 31, 2019	530,062	516,261
Loans, net	23,347,279	21,256,462
Financial liabilities
Deposits	24,849,522	22,813,265
Junior subordinated debt	367,692	406,790
Fair Value, Nonrecurring [Member] | Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Financial assets
Investment securities - HTM, at amortized cost; fair value of $530,062 at March 31, 2020 and $516,261 at December 31, 2019	0	0
Loans, net	0	0
Financial liabilities
Deposits	0	0
Junior subordinated debt	0	0
Fair Value, Nonrecurring [Member] | Estimate of Fair Value Measurement [Member] | Level 2 [Member]
Financial assets
Investment securities - HTM, at amortized cost; fair value of $530,062 at March 31, 2020 and $516,261 at December 31, 2019	530,062	516,261
Loans, net	0	0
Financial liabilities
Deposits	24,849,522	22,813,265
Junior subordinated debt	304,451	332,635
Fair Value, Nonrecurring [Member] | Estimate of Fair Value Measurement [Member] | Level 3 [Member]
Financial assets
Investment securities - HTM, at amortized cost; fair value of $530,062 at March 31, 2020 and $516,261 at December 31, 2019	0	0
Loans, net	23,347,279	21,256,462
Financial liabilities
Deposits	0	0
Junior subordinated debt	63,241	74,155
Fair Value, Recurring [Member]
Financial assets
Investment securities - AFS, at fair value; amortized cost of $3,640,109 at March 31, 2020 and $3,317,928 at December 31, 2019	3,676,651	3,346,310
Investment securities - equity	131,158	138,701
Derivative Asset	4,908	1,903
Financial liabilities
Derivative Liability	95,583	55,570
Fair Value, Recurring [Member] | Level 1 [Member]
Financial assets
Investment securities - AFS, at fair value; amortized cost of $3,640,109 at March 31, 2020 and $3,317,928 at December 31, 2019	28,601	32,167
Investment securities - equity	131,158	138,701
Derivative Asset	0	0
Financial liabilities
Junior subordinated debt	0	0
Derivative Liability	0	0
Fair Value, Recurring [Member] | Level 2 [Member]
Financial assets
Investment securities - AFS, at fair value; amortized cost of $3,640,109 at March 31, 2020 and $3,317,928 at December 31, 2019	3,648,050	3,314,143
Investment securities - equity	0	0
Derivative Asset	4,908	1,903
Financial liabilities
Junior subordinated debt	0	0
Derivative Liability	95,583	55,570
Fair Value, Recurring [Member] | Level 3 [Member]
Financial assets
Investment securities - AFS, at fair value; amortized cost of $3,640,109 at March 31, 2020 and $3,317,928 at December 31, 2019	0	0
Investment securities - equity	0	0
Derivative Asset	0	0
Financial liabilities
Junior subordinated debt	52,990	61,685
Derivative Liability	0	0
Fair Value, Recurring [Member] | Reported Value Measurement [Member]
Financial assets
Investment securities - AFS, at fair value; amortized cost of $3,640,109 at March 31, 2020 and $3,317,928 at December 31, 2019	3,676,651	3,346,310
Investment securities - equity	131,158	138,701
Derivative Asset	4,908	1,903
Accrued Investment Income Receivable	106,777	108,694
Financial liabilities
Customer repurchase agreements	22,980	16,675
Derivative Liability	95,583	55,570
Interest Payable, Current	16,565	24,661
Fair Value, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Financial assets
Investment securities - AFS, at fair value; amortized cost of $3,640,109 at March 31, 2020 and $3,317,928 at December 31, 2019	3,676,651	3,346,310
Investment securities - equity	131,158	138,701
Derivative Asset	4,908	1,903
Accrued Investment Income Receivable	106,777	108,694
Financial liabilities
Customer repurchase agreements	22,980	16,675
Derivative Liability	95,583	55,570
Interest Payable, Current	16,565	24,661
Fair Value, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Level 1 [Member]
Financial assets
Investment securities - AFS, at fair value; amortized cost of $3,640,109 at March 31, 2020 and $3,317,928 at December 31, 2019	28,601	32,167
Investment securities - equity	131,158	138,701
Derivative Asset	0	0
Accrued Investment Income Receivable	0	0
Financial liabilities
Customer repurchase agreements	0	0
Derivative Liability	0	0
Interest Payable, Current	0	0
Fair Value, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Level 2 [Member]
Financial assets
Investment securities - AFS, at fair value; amortized cost of $3,640,109 at March 31, 2020 and $3,317,928 at December 31, 2019	3,648,050	3,314,143
Investment securities - equity	0	0
Derivative Asset	4,908	1,903
Accrued Investment Income Receivable	106,777	108,694
Financial liabilities
Customer repurchase agreements	22,980	16,675
Derivative Liability	95,583	55,570
Interest Payable, Current	16,565	24,661
Fair Value, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Level 3 [Member]
Financial assets
Investment securities - AFS, at fair value; amortized cost of $3,640,109 at March 31, 2020 and $3,317,928 at December 31, 2019	0	0
Investment securities - equity	0	0
Derivative Asset	0	0
Accrued Investment Income Receivable	0	0
Financial liabilities
Customer repurchase agreements	0	0
Derivative Liability	0	0
Interest Payable, Current	$ 0	$ 0