Additional Information Regarding Methods used to Evaluate Loan Portfolio for Impairment (Detail) - Additional Information Loan Portfolio - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Individually evaluated for impairment	$ 35,825	$ 51,954
Loans Receivable, Collectively evaluated for impairment	36,736,594	35,680,191
Total loans, net	38,669,285	37,800,578
Acquired loans with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, other	1,896,866	2,068,433
Mortgage Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Individually evaluated for impairment	25,197	47,480
Loans Receivable, Collectively evaluated for impairment	35,126,712	34,209,870
Total loans, net	36,932,898	36,181,605
Mortgage Receivable | Acquired loans with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, other	1,780,989	1,924,255
Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, Individually evaluated for impairment	10,628	4,474
Loans Receivable, Collectively evaluated for impairment	1,609,882	1,470,321
Total loans, net	1,736,387	1,618,973
Other loans | Acquired loans with deteriorated credit quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable, other	$ 115,877	$ 144,178