Loans and Allowance for Loan Losses - Schedule of Risk Category of Commercial and Commercial Real Estate Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Risk Category Of Loans [Line Items]
Total	$ 12,117,524	$ 12,243,892
Commercial Loan [Member]
Risk Category Of Loans [Line Items]
Total	2,890,296	3,232,970
Commercial Real Estate [Member]
Risk Category Of Loans [Line Items]
Total	5,166,792	4,958,851
Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	713,092	504,625
Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	4,453,700	4,454,226
Pass [Member] | Commercial Loan [Member]
Risk Category Of Loans [Line Items]
Total	2,702,605	3,029,130
Pass [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	665,512	460,158
Pass [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	4,191,455	4,167,902
Criticized [Member] | Commercial Loan [Member]
Risk Category Of Loans [Line Items]
Total	84,676	98,798
Criticized [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	34,651	29,368
Criticized [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	115,514	110,586
Classified - Substandard [Member] | Commercial Loan [Member]
Risk Category Of Loans [Line Items]
Total	63,979	66,394
Classified - Substandard [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total		1,275
Classified - Substandard [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	101,693	102,961
Classified - Nonaccrual [Member] | Commercial Loan [Member]
Risk Category Of Loans [Line Items]
Total	22,240	29,003
Classified - Nonaccrual [Member] | Commercial Real Estate [Member] | Construction [Member]
Risk Category Of Loans [Line Items]
Total	12,929	13,824
Classified - Nonaccrual [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	38,822	37,441
Classified - Doubtful [Member] | Commercial Loan [Member]
Risk Category Of Loans [Line Items]
Total	16,796	9,645
Classified - Doubtful [Member] | Commercial Real Estate [Member] | Other [Member]
Risk Category Of Loans [Line Items]
Total	$ 6,216	$ 35,336