Loans and Allowance for Loan Losses - Schedule of Risk Category of Commercial and Commercial Real Estate Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Risk Category Of Loans [Line Items]
Total	$ 2,962,895	$ 2,717,269	$ 2,001,621
Commercial [Member]
Risk Category Of Loans [Line Items]
Total	2,962,895	2,717,269
Commercial [Member] | Pass [Member]
Risk Category Of Loans [Line Items]
Total	2,815,085	2,577,824
Commercial [Member] | Criticized [Member]
Risk Category Of Loans [Line Items]
Total	70,168	74,876
Commercial [Member] | Classified - Substandard [Member]
Risk Category Of Loans [Line Items]
Total	41,382	37,367
Commercial [Member] | Classified - Nonaccrual [Member]
Risk Category Of Loans [Line Items]
Total	29,390	24,798
Commercial [Member] | Classified - Doubtful [Member]
Risk Category Of Loans [Line Items]
Total	6,870	2,404
Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	490,990	374,306
Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	3,960,782	3,980,246
Commercial Real Estate [Member] | Pass [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	467,663	357,438
Commercial Real Estate [Member] | Pass [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	3,765,884	3,762,896
Commercial Real Estate [Member] | Criticized [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	14,882	14,758
Commercial Real Estate [Member] | Criticized [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	69,841	98,451
Commercial Real Estate [Member] | Classified - Substandard [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	62,595	58,584
Commercial Real Estate [Member] | Classified - Nonaccrual [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	8,445	2,110
Commercial Real Estate [Member] | Classified - Nonaccrual [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	28,376	30,108
Commercial Real Estate [Member] | Classified - Doubtful [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	$ 34,086	$ 30,207