Loans and Allowance for Loan Losses - Schedule of Risk Category of Commercial and Commercial Real Estate Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Risk Category Of Loans [Line Items]
Total	$ 12,046,578	$ 12,243,892	$ 11,295,629
Commercial Loan [Member]
Risk Category Of Loans [Line Items]
Total	3,074,849	3,232,970	2,962,895
Commercial Real Estate [Member]
Risk Category Of Loans [Line Items]
Total	4,993,693	4,958,851	$ 4,451,772
Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	652,903	504,625
Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	4,340,790	4,454,226
Pass [Member] | Commercial Loan [Member]
Risk Category Of Loans [Line Items]
Total	2,902,716	3,029,130
Pass [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	596,761	460,158
Pass [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	4,071,288	4,167,902
Criticized [Member] | Commercial Loan [Member]
Risk Category Of Loans [Line Items]
Total	79,377	98,798
Criticized [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	41,945	29,368
Criticized [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	99,134	110,586
Classified - Substandard [Member] | Commercial Loan [Member]
Risk Category Of Loans [Line Items]
Total	55,446	66,394
Classified - Substandard [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	394	1,275
Classified - Substandard [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	114,695	102,961
Classified - Nonaccrual [Member] | Commercial Loan [Member]
Risk Category Of Loans [Line Items]
Total	28,613	29,003
Classified - Nonaccrual [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	13,803	13,824
Classified - Nonaccrual [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	36,606	37,441
Classified - Doubtful [Member] | Commercial Loan [Member]
Risk Category Of Loans [Line Items]
Total	8,697	9,645
Classified - Doubtful [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	$ 19,067	$ 35,336