Additional Information Regarding Methods used to Evaluate Loan Portfolio for Impairment (Detail) - Additional Information Loan Portfolio - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Individually evaluated for impairment	$ 75,113	$ 48,252
Loans Receivable, Collectively evaluated for impairment	37,405,591	37,302,187
Total loans, net	37,480,704	39,054,334
Acquired loans with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, other		1,703,895
Mortgage Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Individually evaluated for impairment	29,431	29,660
Loans Receivable, Collectively evaluated for impairment	35,465,464	35,402,029
Total loans, net	35,494,895	37,046,444
Mortgage Receivable | Acquired loans with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, other		1,614,755
Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Individually evaluated for impairment	45,682	18,592
Loans Receivable, Collectively evaluated for impairment	1,940,127	1,900,158
Total loans, net	$ 1,985,809	2,007,890
Other loans | Acquired loans with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, other		$ 89,140