Securities (Detail 2) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Expected remaining maturities of debt securities available-for-sale, fair value
Fair Value	$ 4,940,843	$ 5,882,983
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Total of debt securities held-to-maturity, amortized cost	3,422,179	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	885,091
Securities available-for-sale, Over 1 year through 5 years, fair value	3,874,414
Securities available-for-sale, Over 5 years through 10 years, fair value	177,524
Securities available-for-sale, Over 10 years, fair value	3,348
Fair Value	4,940,377	5,879,837
Expected remaining maturities of debt securities available-for-sale, amortized cost
Securities available-for-sale, One year or less, amortized cost	882,733
Securities available-for-sale, Over 1 year through 5 years, amortized cost	3,877,641
Securities available-for-sale, Over 5 years through 10 years, amortized cost	178,695
Securities available-for-sale, Over 10 years, amortized cost	3,400
Total of debt securities available-for-sale, amortized cost	4,942,469
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, One year or less, amortized cost	9,728
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	1,061,118
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	1,989,399
Securities held-to-maturity, Over 10 years, amortized cost	361,934
Total of debt securities held-to-maturity, amortized cost	3,422,179
U.S. Treasury
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, One year or less, fair value	72,793
Securities available-for-sale, Over 1 year through 5 years, fair value	75,515
Fair Value	148,308	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	476,226
Securities available-for-sale, Over 1 year through 5 years, fair value	423,708
Fair Value	899,934	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	23,000
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	149,266
Securities held-to-maturity, Over 10 years, amortized cost	151,539
Total of debt securities held-to-maturity, amortized cost	323,805	292,932
Federal agency - MBS
Expected remaining maturities of debt securities available-for-sale, fair value
Securities available-for-sale, Over 1 year through 5 years, fair value	96,878
Fair Value	96,878	104,526
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	47,500
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	526,581
Securities held-to-maturity, Over 10 years, amortized cost	4,522
Total of debt securities held-to-maturity, amortized cost	578,603	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	120,247
Securities available-for-sale, Over 1 year through 5 years, fair value	2,988,305
Securities available-for-sale, Over 5 years through 10 years, fair value	177,524
Fair Value	3,286,076	3,580,590
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, One year or less, amortized cost	9,728
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	762,883
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	912,076
Total of debt securities held-to-maturity, amortized cost	1,684,687	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	1,223
Securities available-for-sale, Over 1 year through 5 years, fair value	20,508
Fair Value	21,731	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	175,966
Securities available-for-sale, Over 1 year through 5 years, fair value	220,741
Securities available-for-sale, Over 10 years, fair value	3,348
Fair Value	400,055	479,031
Expected remaining maturities of debt securities held-to-maturity, amortized cost
Securities held-to-maturity, Over 1 year through 5 years, amortized cost	141,904
Securities held-to-maturity, Over 5 years through 10 years, amortized cost	401,476
Securities held-to-maturity, Over 10 years, amortized cost	205,873
Total of debt securities held-to-maturity, amortized cost	749,253	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	38,636
Securities available-for-sale, Over 1 year through 5 years, fair value	48,759
Fair Value	87,395	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	85,831
Total of debt securities held-to-maturity, amortized cost	$ 85,831	$ 86,231