Loans and Allowance for Credit Losses - Schedule of Risk Category of Commercial and Commercial Real Estate Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Risk Category Of Loans [Line Items]
Total	$ 1,893,700	$ 1,804,615	$ 1,775,954
Commercial [Member]
Risk Category Of Loans [Line Items]
Total	1,893,700	1,814,940
Commercial [Member] | Pass [Member]
Risk Category Of Loans [Line Items]
Total	1,774,857	1,672,672
Commercial [Member] | Criticized [Member]
Risk Category Of Loans [Line Items]
Total	38,867	55,570
Commercial [Member] | Classified - Substandard [Member]
Risk Category Of Loans [Line Items]
Total	25,422	24,723
Commercial [Member] | Classified - Nonaccrual [Member]
Risk Category Of Loans [Line Items]
Total	52,226	58,469
Commercial [Member] | Classified - Doubtful [Member]
Risk Category Of Loans [Line Items]
Total	2,328	3,506
Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	263,496	188,688
Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	2,680,029	1,680,284
Commercial Real Estate [Member] | Pass [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	256,427	182,701
Commercial Real Estate [Member] | Pass [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	2,484,795	1,508,309
Commercial Real Estate [Member] | Criticized [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	4,014	3,300
Commercial Real Estate [Member] | Criticized [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	64,005	75,477
Commercial Real Estate [Member] | Classified - Substandard [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	1,572	1,857
Commercial Real Estate [Member] | Classified - Substandard [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	56,982	49,091
Commercial Real Estate [Member] | Classified - Nonaccrual [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	1,483	830
Commercial Real Estate [Member] | Classified - Nonaccrual [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	64,338	39,521
Commercial Real Estate [Member] | Classified - Doubtful [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	$ 9,909	$ 7,886