Securities (Detail 2) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Expected remaining maturities of debt securities available-for-sale, fair value
Fair Value	$ 5,309,187	$ 5,882,983
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Total of debt securities held-to-maturity, amortized cost	3,506,455	3,427,031
Total debt securities
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	863,802
Securities available-for-sale, Over 1 year through 5 years, fair value	4,268,028
Securities available-for-sale, Over 5 years through 10 years, fair value	173,986
Securities available-for-sale, Over 10 years, fair value	3,371
Fair Value	5,309,187	5,879,837
Expected remaining maturities of debt securities available-for-sale, amortized cost
Securities available-for-sale, One year or less, amortized cost	861,509
Securities available-for-sale, Over 1 year through 5 years, amortized cost	4,264,720
Securities available-for-sale, Over 5 years through 10 years, amortized cost	174,371
Securities available-for-sale, Over 10 years, amortized cost	3,400
Total of debt securities available-for-sale, amortized cost	5,304,000
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, One year or less, amortized cost	9,631
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	1,189,769
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	2,011,485
Securities held-to-maturity, Over 10 years, amortized cost	295,570
Total of debt securities held-to-maturity, amortized cost	3,506,455
U.S. Treasury
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	269,754
Securities available-for-sale, Over 1 year through 5 years, fair value	120,575
Fair Value	390,329	116,926
Federal agency - Debt
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	179,603
Securities available-for-sale, Over 1 year through 5 years, fair value	106,757
Fair Value	286,360	1,398,581
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	45,000
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	209,125
Securities held-to-maturity, Over 10 years, amortized cost	191,596
Total of debt securities held-to-maturity, amortized cost	445,721	292,932
Federal agency - MBS
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	1,819
Securities available-for-sale, Over 1 year through 5 years, fair value	91,062
Fair Value	92,881	104,526
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, One year or less, amortized cost	10
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	74,949
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	495,583
Securities held-to-maturity, Over 10 years, amortized cost	4,529
Total of debt securities held-to-maturity, amortized cost	575,071	553,589
CMOs - Federal agency
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	119,443
Securities available-for-sale, Over 1 year through 5 years, fair value	3,248,817
Securities available-for-sale, Over 5 years through 10 years, fair value	167,868
Fair Value	3,536,128	3,580,590
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, One year or less, amortized cost	8,724
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	773,640
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	848,024
Total of debt securities held-to-maturity, amortized cost	1,630,388	1,811,574
CMOs - Non-agency
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	1,079
Securities available-for-sale, Over 1 year through 5 years, fair value	13,234
Securities available-for-sale, Over 5 years through 10 years, fair value	6,118
Fair Value	20,431	24,014
State and municipal
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	165,254
Securities available-for-sale, Over 1 year through 5 years, fair value	192,119
Securities available-for-sale, Over 10 years, fair value	3,371
Fair Value	360,744	479,031
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, One year or less, amortized cost	897
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	210,551
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	458,753
Securities held-to-maturity, Over 10 years, amortized cost	99,445
Total of debt securities held-to-maturity, amortized cost	769,646	682,705
Other debt securities
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	126,850
Securities available-for-sale, Over 1 year through 5 years, fair value	495,464
Fair Value	622,314	176,169
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	85,629
Total of debt securities held-to-maturity, amortized cost	$ 85,629	$ 86,231