Loans and Allowance for Loan Losses - Schedule of Risk Category of Commercial and Commercial Real Estate Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Risk Category Of Loans [Line Items]
Total	$ 3,042,790	$ 3,232,970	$ 2,811,629
Commercial [Member]
Risk Category Of Loans [Line Items]
Total	3,042,790	3,232,970
Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	552,825	504,625
Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	4,470,795	4,454,226
Pass [Member] | Commercial [Member]
Risk Category Of Loans [Line Items]
Total	2,837,646	3,029,130
Pass [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	494,410	460,158
Pass [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	4,140,815	4,167,902
Criticized [Member] | Commercial [Member]
Risk Category Of Loans [Line Items]
Total	106,501	98,798
Criticized [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	43,161	29,368
Criticized [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	119,173	110,586
Classified - Substandard [Member] | Commercial [Member]
Risk Category Of Loans [Line Items]
Total	64,597	66,394
Classified - Substandard [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	746	1,275
Classified - Substandard [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	141,357	102,961
Classified - Nonaccrual [Member] | Commercial [Member]
Risk Category Of Loans [Line Items]
Total	22,982	29,003
Classified - Nonaccrual [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	14,508	13,824
Classified - Nonaccrual [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	33,870	37,441
Classified - Doubtful [Member] | Commercial [Member]
Risk Category Of Loans [Line Items]
Total	11,064	9,645
Classified - Doubtful [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	$ 35,580	$ 35,336