Securities (Detail 4) $ in Thousands	Jun. 30, 2015 USD ($) security item	Dec. 31, 2014 USD ($) security item
Securities available-for-sale:
Securities available-for-sale, Fair Value, Less than 12 months	$ 1,273,046	$ 2,027,804
Securities available-for-sale, Estimated Unrealized Loss, Less than 12 months	3,657	6,728
Securities available-for-sale, Fair Value, 12 months or greater	1,270,211	1,472,436
Securities available-for-sale, Estimated Unrealized Loss, 12 months or greater	27,144	37,586
Securities available-for-sale, Fair Value, Total	2,543,257	3,500,240
Securities available-for-sale, Estimated Unrealized Loss, Total	30,801	44,314
Securities held-to-maturity:
Securities held-to-maturity, Fair Value, Less than 12 months	822,602	283,478
Securities held-to-maturity, Estimated Unrealized Loss, Less than 12 months	12,560	2,568
Securities held-to-maturity, Fair Value, 12 months or greater	300,169	824,838
Securities held-to-maturity, Estimated Unrealized Loss, 12 months or greater	7,212	12,475
Securities held-to-maturity, Fair Value, Total	1,122,771	1,108,316
Securities held-to-maturity, Estimated Unrealized Loss, Total	19,772	15,043
U.S. Treasury
Securities available-for-sale:
Securities available-for-sale, Fair Value, Less than 12 months	89,266	15,814
Securities available-for-sale, Estimated Unrealized Loss, Less than 12 months	14	10
Securities available-for-sale, Fair Value, Total	89,266	15,814
Securities available-for-sale, Estimated Unrealized Loss, Total	$ 14	$ 10
Other information
Number of available-for-sale and held-to-maturity securities in the unrealized loss position | security	4	2
Federal agency - Debt
Securities available-for-sale:
Securities available-for-sale, Fair Value, Less than 12 months	$ 307,112	$ 1,008,234
Securities available-for-sale, Estimated Unrealized Loss, Less than 12 months	207	2,622
Securities available-for-sale, Fair Value, 12 months or greater		135,868
Securities available-for-sale, Estimated Unrealized Loss, 12 months or greater		658
Securities available-for-sale, Fair Value, Total	307,112	1,144,102
Securities available-for-sale, Estimated Unrealized Loss, Total	207	3,280
Securities held-to-maturity:
Securities held-to-maturity, Fair Value, Less than 12 months	27,656
Securities held-to-maturity, Estimated Unrealized Loss, Less than 12 months	68
Securities held-to-maturity, Fair Value, 12 months or greater	5,668	26,316
Securities held-to-maturity, Estimated Unrealized Loss, 12 months or greater	98	255
Securities held-to-maturity, Fair Value, Total	33,324	26,316
Securities held-to-maturity, Estimated Unrealized Loss, Total	$ 166	$ 255
Other information
Number of available-for-sale and held-to-maturity securities in the unrealized loss position | security	10	37
Federal agency - MBS
Securities available-for-sale:
Securities available-for-sale, Fair Value, Less than 12 months		$ 35
Securities available-for-sale, Fair Value, 12 months or greater	$ 54,924	57,970
Securities available-for-sale, Estimated Unrealized Loss, 12 months or greater	1,039	1,014
Securities available-for-sale, Fair Value, Total	54,924	58,005
Securities available-for-sale, Estimated Unrealized Loss, Total	1,039	1,014
Securities held-to-maturity:
Securities held-to-maturity, Fair Value, Less than 12 months	130,389	4,800
Securities held-to-maturity, Estimated Unrealized Loss, Less than 12 months	2,014	21
Securities held-to-maturity, Fair Value, 12 months or greater	39,975	114,856
Securities held-to-maturity, Estimated Unrealized Loss, 12 months or greater	1,091	2,254
Securities held-to-maturity, Fair Value, Total	170,364	119,656
Securities held-to-maturity, Estimated Unrealized Loss, Total	$ 3,105	$ 2,275
Other information
Number of available-for-sale and held-to-maturity securities in the unrealized loss position | security	28	23
CMOs - Federal agency
Securities available-for-sale:
Securities available-for-sale, Fair Value, Less than 12 months	$ 718,502	$ 871,026
Securities available-for-sale, Estimated Unrealized Loss, Less than 12 months	3,031	3,417
Securities available-for-sale, Fair Value, 12 months or greater	1,200,002	1,261,695
Securities available-for-sale, Estimated Unrealized Loss, 12 months or greater	25,690	35,452
Securities available-for-sale, Fair Value, Total	1,918,504	2,132,721
Securities available-for-sale, Estimated Unrealized Loss, Total	28,721	38,869
Securities held-to-maturity:
Securities held-to-maturity, Fair Value, Less than 12 months	400,181	202,014
Securities held-to-maturity, Estimated Unrealized Loss, Less than 12 months	3,376	2,247
Securities held-to-maturity, Fair Value, 12 months or greater	221,525	588,019
Securities held-to-maturity, Estimated Unrealized Loss, 12 months or greater	4,104	8,045
Securities held-to-maturity, Fair Value, Total	621,706	790,033
Securities held-to-maturity, Estimated Unrealized Loss, Total	$ 7,480	$ 10,292
Other information
Number of available-for-sale and held-to-maturity securities in the unrealized loss position | security	131	141
CMOs - Non-agency
Securities available-for-sale:
Securities available-for-sale, Fair Value, Less than 12 months	$ 6,342	$ 1,949
Securities available-for-sale, Estimated Unrealized Loss, Less than 12 months	19	15
Securities available-for-sale, Fair Value, 12 months or greater	11,738	12,720
Securities available-for-sale, Estimated Unrealized Loss, 12 months or greater	362	396
Securities available-for-sale, Fair Value, Total	18,080	14,669
Securities available-for-sale, Estimated Unrealized Loss, Total	$ 381	$ 411
Other information
Number of available-for-sale and held-to-maturity securities in the unrealized loss position | security	4	3
State and municipal
Securities available-for-sale:
Securities available-for-sale, Fair Value, Less than 12 months	$ 151,358	$ 130,208
Securities available-for-sale, Estimated Unrealized Loss, Less than 12 months	188	314
Securities available-for-sale, Fair Value, 12 months or greater	3,547	4,183
Securities available-for-sale, Estimated Unrealized Loss, 12 months or greater	53	66
Securities available-for-sale, Fair Value, Total	154,905	134,391
Securities available-for-sale, Estimated Unrealized Loss, Total	241	380
Securities held-to-maturity:
Securities held-to-maturity, Fair Value, Less than 12 months	264,376	14,851
Securities held-to-maturity, Estimated Unrealized Loss, Less than 12 months	7,102	76
Securities held-to-maturity, Fair Value, 12 months or greater	33,001	95,647
Securities held-to-maturity, Estimated Unrealized Loss, 12 months or greater	1,919	1,921
Securities held-to-maturity, Fair Value, Total	297,377	110,498
Securities held-to-maturity, Estimated Unrealized Loss, Total	$ 9,021	$ 1,997
Other information
Number of available-for-sale and held-to-maturity securities in the unrealized loss position | security	376	225
Other debt securities
Securities held-to-maturity:
Securities held-to-maturity, Fair Value, Less than 12 months		$ 61,813
Securities held-to-maturity, Estimated Unrealized Loss, Less than 12 months		224
Securities held-to-maturity, Fair Value, Total		61,813
Securities held-to-maturity, Estimated Unrealized Loss, Total		$ 224
Other information
Number of available-for-sale and held-to-maturity securities in the unrealized loss position | security		5
Total debt securities
Securities available-for-sale:
Securities available-for-sale, Fair Value, Less than 12 months	$ 1,272,580	$ 2,027,266
Securities available-for-sale, Estimated Unrealized Loss, Less than 12 months	3,459	6,378
Securities available-for-sale, Fair Value, 12 months or greater	1,270,211	1,472,436
Securities available-for-sale, Estimated Unrealized Loss, 12 months or greater	27,144	37,586
Securities available-for-sale, Fair Value, Total	2,542,791	3,499,702
Securities available-for-sale, Estimated Unrealized Loss, Total	$ 30,603	$ 43,964
Other information
Number of available-for-sale and held-to-maturity securities in the unrealized loss position | security	553	436
Equity securities and mutual funds
Securities available-for-sale:
Securities available-for-sale, Fair Value, Less than 12 months	$ 466	$ 538
Securities available-for-sale, Estimated Unrealized Loss, Less than 12 months	198	350
Securities available-for-sale, Fair Value, Total	466	538
Securities available-for-sale, Estimated Unrealized Loss, Total	$ 198	$ 350
Other information
Number of available-for-sale and held-to-maturity securities in the unrealized loss position | item	1	1