Loans and Allowance for Loan Losses - Schedule of Risk Category of Commercial and Commercial Real Estate Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Commercial [Member]
Risk Category Of Loans [Line Items]
Total	$ 3,232,970	$ 2,717,269
Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	504,625	374,306
Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	4,454,226	3,980,246
Pass [Member] | Commercial [Member]
Risk Category Of Loans [Line Items]
Total	3,029,130	2,577,824
Pass [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	460,158	357,438
Pass [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	4,167,902	3,762,896
Criticized [Member] | Commercial [Member]
Risk Category Of Loans [Line Items]
Total	98,798	74,876
Criticized [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	29,368	14,758
Criticized [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	110,586	98,451
Classified - Substandard [Member] | Commercial [Member]
Risk Category Of Loans [Line Items]
Total	66,394	37,367
Classified - Substandard [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	1,275	0
Classified - Substandard [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	102,961	58,584
Classified - Nonaccrual [Member] | Commercial [Member]
Risk Category Of Loans [Line Items]
Total	29,003	24,798
Classified - Nonaccrual [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	13,824	2,110
Classified - Nonaccrual [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	37,441	30,108
Classified - Doubtful [Member] | Commercial [Member]
Risk Category Of Loans [Line Items]
Total	9,645	2,404
Classified - Doubtful [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	0	0
Classified - Doubtful [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	$ 35,336	$ 30,207