Fair Value Measurements (Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	$ 5,895,436	$ 6,203,299
Trading account securities	16,398	30,074
Derivative assets:	16,265	2,246
Derivative liabilities:	42,603	74,159
US Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	2,540,554	3,057,921
Trading account securities	15,389	14,038
US Government agencies/ corporations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	53,980
Residential Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	1,776,016	2,518,003
States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	1,488,914	591,483
Trading account securities	1,009	16,036
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	35,972	35,892
Interest Rate Swaps, Caps and Floors [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	44,694	60,890
Derivative liabilities:	47,542	72,557
Commodity Swaps And Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	10,026	3,867
Derivative liabilities:	9,712	3,772
Foreign Currency Forward Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	135	3
Derivative liabilities:	85
Level 1 [Member] | US Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	2,540,554	3,057,921
Trading account securities	15,389	14,038
Level 1 [Member] | Foreign Currency Forward Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	135	3
Derivative liabilities:	85
Level 2 [Member] | US Government agencies/ corporations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	53,980
Level 2 [Member] | Residential Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	1,776,016	2,518,003
Level 2 [Member] | States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	1,488,914	591,483
Trading account securities	1,009	16,036
Level 2 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	35,972	35,892
Level 2 [Member] | Interest Rate Swaps, Caps and Floors [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	44,520	60,535
Derivative liabilities:	47,542	72,557
Level 2 [Member] | Commodity Swaps And Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	10,026	3,867
Derivative liabilities:	9,712	3,772
Level 3 [Member] | Interest Rate Swaps, Caps and Floors [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	$ 174	$ 355