Loans and Allowance for Loan Losses - Schedule of Risk Category of Commercial and Commercial Real Estate Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Commercial [Member]
Risk Category Of Loans [Line Items]
Total	$ 2,717,269	$ 1,917,099
Commercial [Member] | Pass [Member]
Risk Category Of Loans [Line Items]
Total	2,577,824	1,750,922
Commercial [Member] | Criticized [Member]
Risk Category Of Loans [Line Items]
Total	74,876	45,614
Commercial [Member] | Classified - Substandard [Member]
Risk Category Of Loans [Line Items]
Total	37,367	63,978
Commercial [Member] | Classified - Nonaccrual [Member]
Risk Category Of Loans [Line Items]
Total	24,798	53,063
Commercial [Member] | Classified - Doubtful [Member]
Risk Category Of Loans [Line Items]
Total	2,404	3,522
Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	374,306	357,802
Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	3,980,246	2,773,051
Commercial Real Estate [Member] | Pass [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	357,438	347,325
Commercial Real Estate [Member] | Pass [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	3,762,896	2,669,890
Commercial Real Estate [Member] | Criticized [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	14,758	9,258
Commercial Real Estate [Member] | Criticized [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	98,451	40,590
Commercial Real Estate [Member] | Classified - Substandard [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total		49
Commercial Real Estate [Member] | Classified - Substandard [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	58,584	19,715
Commercial Real Estate [Member] | Classified - Nonaccrual [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	2,110	1,170
Commercial Real Estate [Member] | Classified - Nonaccrual [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	30,108	33,833
Commercial Real Estate [Member] | Classified - Doubtful [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	$ 30,207	$ 9,023