Condensed Financial Statements of Parent Company (Schedule of Condensed Balance Sheets) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Cash	$ 532,824	$ 702,485
Resell agreements	66,917	30,792
Cash and cash equivalents	3,591,523	4,364,123	$ 4,556,125	$ 3,524,979
Total assets	28,567,118	28,277,775
Junior subordinated deferrable interest debentures	137,115	137,115
Accrued interest payable and other liabilities	202,543	250,208
Total liabilities	25,676,775	25,426,372
Shareholders’ Equity	2,890,343	2,851,403	$ 2,514,161	$ 2,417,482
Total liabilities and shareholders’ equity	28,567,118	28,277,775
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Cash	6,434	7,335
Resell agreements	200,100	286,660
Cash and cash equivalents	206,534	293,995
Investment in subsidiaries	2,920,506	2,791,647
Accrued interest receivable and other assets	36,578	29,705
Total assets	3,163,618	3,115,347
Junior subordinated deferrable interest debentures	137,115	137,115
Subordinated notes payable	100,000	100,000
Accrued interest payable and other liabilities	36,160	26,829
Total liabilities	273,275	263,944
Shareholders’ Equity	2,890,343	2,851,403
Total liabilities and shareholders’ equity	$ 3,163,618	$ 3,115,347