Condensed Financial Statements of Parent Company (Schedule of Condensed Balance Sheets) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Cash	$ 581,857	$ 678,791
Resell agreements	356,374	635,017
Cash and cash equivalents	3,788,181	3,955,779	$ 5,053,047	$ 4,141,445
Total assets	34,027,428	32,292,966
Junior subordinated deferrable interest debentures, net of unamortized issuance costs	136,299	136,242
Subordinated notes, net of unamortized issuance costs	98,865	98,708
Accrued interest payable and other liabilities	545,690	172,347
Total liabilities	30,115,760	28,924,049
Shareholders’ Equity	3,911,668	3,368,917	$ 3,297,863	$ 3,002,528
Total liabilities and shareholders’ equity	34,027,428	32,292,966
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Cash	9,116	11,397
Resell agreements	258,000	225,000
Cash and cash equivalents	267,116	236,397
Investment in subsidiaries	3,896,962	3,362,474
Accrued interest receivable and other assets	2,545	9,122
Total assets	4,166,623	3,607,993
Junior subordinated deferrable interest debentures, net of unamortized issuance costs	136,299	136,242
Subordinated notes, net of unamortized issuance costs	98,865	98,708
Accrued interest payable and other liabilities	19,791	4,126
Total liabilities	254,955	239,076
Shareholders’ Equity	3,911,668	3,368,917
Total liabilities and shareholders’ equity	$ 4,166,623	$ 3,607,993