Condensed Financial Statements of Parent Company (Schedule of Condensed Balance Sheets) (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Cash	$ 885,121,000	$ 790,106,000
Resell agreements	24,248,000	84,448,000
Total cash and cash equivalents	4,556,125,000	3,524,979,000
Other assets	284,537,000	292,346,000
Total assets	24,312,939,000	23,124,069,000
Junior subordinated deferrable interest debentures	123,712,000	123,712,000
Accrued interest payable and other liabilities	218,027,000	424,441,000
Total liabilities	21,798,778,000	20,706,587,000
Shareholders’ Equity	2,514,161,000	2,417,482,000	2,283,537,000	2,061,680,000
Total liabilities and shareholders’ equity	24,312,939,000	23,124,069,000
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Cash	7,477,000	8,601,000
Resell agreements	320,200,000	222,460,000
Total cash and cash equivalents	327,677,000	231,061,000
Investment in subsidiaries	2,409,433,000	2,410,227,000
Other assets	19,038,000	6,260,000
Total assets	2,756,148,000	2,647,548,000
Junior subordinated deferrable interest debentures	123,712,000	123,712,000
Subordinated notes payable	100,000,000	100,000,000
Accrued interest payable and other liabilities	18,275,000	6,354,000
Total liabilities	241,987,000	230,066,000
Shareholders’ Equity	2,514,161,000	2,417,482,000
Total liabilities and shareholders’ equity	$ 2,756,148,000	$ 2,647,548,000