Investment Securities - Amortized Cost and Estimated Fair Value of Investment Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Dec. 30, 2013
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Other securities, Amortized cost	$ 328,536	$ 298,581	$ 298,581
Other securities, Estimated fair value	328,536	298,581	298,581
Investment securities, available for sale, amortized cost	9,175,295	4,444,365
Investment securities available for sale, gross unrealized gains	227,607	127,333
Investment securities available for sale, gross unrealized losses	18,885	39,912
Investment securities available for sale, estimated fair value	9,384,017	4,531,786
Amortized cost for held to maturity	3,635,815	3,966,130
Gross unrealized gains for held to maturity	53,761	19,904
Gross unrealized losses for held to maturity	68,185	125,907
Estimated fair value for held to maturity	3,621,391	3,860,127
Total Amortized cost	13,139,646	8,709,076
Total for Gross unrealized gains	281,368	147,237
Total for Gross unrealized losses	87,070	165,819
Total for Estimated fair value	13,333,944	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	8,751,108	4,123,435
Investment securities available for sale, gross unrealized gains	145,708	61,001
Investment securities available for sale, gross unrealized losses	2,765	19,350
Investment securities available for sale, estimated fair value	8,894,051	4,165,086
Amortized cost for held to maturity	3,269,344	3,567,905
Gross unrealized gains for held to maturity	50,477	16,160
Gross unrealized losses for held to maturity	18,196	65,149
Estimated fair value for held to maturity	3,301,625	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	112	1,468
Investment securities available for sale, gross unrealized gains	4	387
Investment securities available for sale, gross unrealized losses	4	5
Investment securities available for sale, estimated fair value	112	1,850
Amortized cost for held to maturity	206,695	219,628
Gross unrealized gains for held to maturity
Gross unrealized losses for held to maturity	49,897	60,623
Estimated fair value for held to maturity	156,798	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	30,788	42,274
Investment securities available for sale, gross unrealized gains	24,383	21,666
Investment securities available for sale, gross unrealized losses	363	857
Investment securities available for sale, estimated fair value	54,808	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	9,174	10,484
Investment securities available for sale, gross unrealized gains	270	333
Investment securities available for sale, gross unrealized losses	53	6
Investment securities available for sale, estimated fair value	9,391	10,811
Amortized cost for held to maturity	151,789	169,684
Gross unrealized gains for held to maturity	3,284	3,744
Gross unrealized losses for held to maturity	92	135
Estimated fair value for held to maturity	154,981	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	138,278	137,828
Investment securities available for sale, gross unrealized gains	2,304	1,722
Investment securities available for sale, gross unrealized losses	15,183	19,465
Investment securities available for sale, estimated fair value	125,399	120,085
Amortized cost for held to maturity	7,987	8,913
Gross unrealized gains for held to maturity
Gross unrealized losses for held to maturity
Estimated fair value for held to maturity	7,987	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	166,092	37,396
Investment securities available for sale, gross unrealized gains	206	382
Investment securities available for sale, gross unrealized losses	111	2
Investment securities available for sale, estimated fair value	166,187	37,776
Equity Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Investment securities, available for sale, amortized cost	79,743	91,480
Investment securities available for sale, gross unrealized gains	54,732	41,842
Investment securities available for sale, gross unrealized losses	406	227
Investment securities available for sale, estimated fair value	$ 134,069	$ 133,095