Condensed Financial Statements of Parent Company (Schedule of Condensed Balance Sheets) (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Cash	$ 561,838	$ 532,824
Resell agreements	18,742	66,917
Cash and cash equivalents	4,141,445	3,591,523	$ 4,364,123	$ 4,556,125
Total assets	30,196,319	28,565,942
Junior subordinated deferrable interest debentures	136,127	136,069
Accrued interest payable and other liabilities	169,107	202,543
Total liabilities	27,193,791	25,675,599
Shareholders’ Equity	3,002,528	2,890,343	$ 2,851,403	$ 2,514,161
Total liabilities and shareholders’ equity	30,196,319	28,565,942
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Cash	9,854	6,434
Resell agreements	279,270	200,100
Cash and cash equivalents	289,124	206,534
Investment in subsidiaries	2,949,346	2,920,506
Accrued interest receivable and other assets	5,799	35,402
Total assets	3,244,269	3,162,442
Junior subordinated deferrable interest debentures	136,127	136,069
Subordinated notes payable	99,990	99,870
Accrued interest payable and other liabilities	5,624	36,160
Total liabilities	241,741	272,099
Shareholders’ Equity	3,002,528	2,890,343
Total liabilities and shareholders’ equity	$ 3,244,269	$ 3,162,442