Investment Securities - Amortized Cost and Estimated Fair Value of Investment Securities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Other securities, Amortized cost	$ 298,693	$ 298,581
Other securities, Gross unrealized gains
Other securities, Gross unrealized losses
Other securities, Estimated fair value	298,693	298,581
Investment securities, available for sale, amortized cost	6,042,063	4,444,365
Gross unrealized gains	175,169	127,333
Gross unrealized losses	25,661	39,912
Estimated fair value	6,191,571	4,531,786
Amortized cost for held to maturity	3,873,985	3,966,130
Gross unrealized gains for held to maturity	30,127	19,904
Gross unrealized losses for held to maturity	89,346	125,907
Estimated fair value for held to maturity	3,814,766	3,860,127
Total Amortized cost	10,214,741	8,709,076
Total for Gross unrealized gains	205,296	147,237
Total for Gross unrealized losses	115,007	165,819
Total for Estimated fair value	10,305,030	8,690,494
Government Issued or Guaranteed [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities, available for sale, amortized cost	5,722,948	4,123,435
Gross unrealized gains	85,193	61,001
Gross unrealized losses	7,050	19,350
Estimated fair value	5,801,091	4,165,086
Amortized cost for held to maturity	3,486,786	3,567,905
Gross unrealized gains for held to maturity	26,847	16,160
Gross unrealized losses for held to maturity	37,718	65,149
Estimated fair value for held to maturity	3,475,915	3,518,916
Privately issued [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities, available for sale, amortized cost	235	1,468
Gross unrealized gains	466	387
Gross unrealized losses	5	5
Estimated fair value	696	1,850
Amortized cost for held to maturity	215,649	219,628
Gross unrealized gains for held to maturity
Gross unrealized losses for held to maturity	51,434	60,623
Estimated fair value for held to maturity	164,215	159,005
Collateralized Debt Obligations [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities, available for sale, amortized cost	38,451	42,274
Gross unrealized gains	23,623	21,666
Gross unrealized losses	306	857
Estimated fair value	61,768	63,083
Obligations of States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities, available for sale, amortized cost	10,148	10,484
Gross unrealized gains	306	333
Gross unrealized losses	71	6
Estimated fair value	10,383	10,811
Amortized cost for held to maturity	162,894	169,684
Gross unrealized gains for held to maturity	3,280	3,744
Gross unrealized losses for held to maturity	194	135
Estimated fair value for held to maturity	165,980	173,293
Other Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities, available for sale, amortized cost	138,197	137,828
Gross unrealized gains	1,859	1,722
Gross unrealized losses	17,807	19,465
Estimated fair value	122,249	120,085
Amortized cost for held to maturity	8,656	8,913
Gross unrealized gains for held to maturity
Gross unrealized losses for held to maturity
Estimated fair value for held to maturity	8,656	8,913
U.S. Treasury and Federal Agencies [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities, available for sale, amortized cost	42,415	37,396
Gross unrealized gains	291	382
Gross unrealized losses	59	2
Estimated fair value	42,647	37,776
Equity Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities, available for sale, amortized cost	89,669	91,480
Gross unrealized gains	63,431	41,842
Gross unrealized losses	363	227
Estimated fair value	$ 152,737	$ 133,095