Additional Information Regarding Methods used to Evaluate Loan Portfolio for Impairment (Detail) - Additional Information Loan Portfolio - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Individually evaluated for impairment	$ 63,934	$ 88,380
Loans Receivable, Collectively evaluated for impairment	34,047,995	32,915,981
Total loans, net	36,273,960	35,432,983
Acquired loans with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, other	2,162,031	2,428,622
Mortgage Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Individually evaluated for impairment	59,187	81,574
Loans Receivable, Collectively evaluated for impairment	32,616,459	31,781,623
Total loans, net	34,681,134	34,090,769
Mortgage Receivable | Acquired loans with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, other	2,005,488	2,227,572
Other loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Individually evaluated for impairment	4,747	6,806
Loans Receivable, Collectively evaluated for impairment	1,431,536	1,134,358
Total loans, net	1,592,826	1,342,214
Other loan | Acquired loans with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, other	$ 156,543	$ 201,050