Investment Securities (Summary Of Investment Securities) (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Available-for-sale Securities [Abstract]
Amortized Cost	$ 2,831,091	$ 3,015,763
Unrealized Gains	12,853	16,226
Unrealized Losses	(35,978)	(40,898)
Fair Value	2,807,966	2,991,091
Held-to-maturity Securities [Abstract]
Amortized Cost	4,219,198	4,160,658
Unrealized Gains	34,049	37,567
Unrealized Losses	(55,869)	(73,100)
Fair Value	4,197,378	4,125,125
US Treasury Bill Securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	3,843	734
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	3,843	734
Agency collateralized mortgage obligations (CMOs) [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	359,075	419,865
Unrealized Gains	3,064	3,344
Unrealized Losses	(3,123)	(3,503)
Fair Value	359,016	419,706
Held-to-maturity Securities [Abstract]
Amortized Cost	297,649	339,455
Unrealized Gains	1,381	1,977
Unrealized Losses	(3,170)	(3,824)
Fair Value	295,860	337,608
Agency mortgage-backed securities (MBS) [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	888,810	969,460
Unrealized Gains	3,764	4,398
Unrealized Losses	(16,884)	(19,509)
Fair Value	875,690	954,349
Held-to-maturity Securities [Abstract]
Amortized Cost	2,324,270	2,317,449
Unrealized Gains	23,383	26,388
Unrealized Losses	(35,115)	(41,768)
Fair Value	2,312,538	2,302,069
Agency commercial mortgage-backed securities (ACMBS) [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	602,446	587,776
Unrealized Gains	0	63
Unrealized Losses	(15,344)	(14,567)
Fair Value	587,102	573,272
Held-to-maturity Securities [Abstract]
Amortized Cost	642,676	547,726
Unrealized Gains	309	694
Unrealized Losses	(2,727)	(1,348)
Fair Value	640,258	547,072
Non-agency Commercial mortgage-backed securities (CMBS) [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	477,932	473,974
Unrealized Gains	2,202	4,093
Unrealized Losses	(226)	(702)
Fair Value	479,908	477,365
Held-to-maturity Securities [Abstract]
Amortized Cost	265,086	298,538
Unrealized Gains	3,862	4,107
Unrealized Losses	(252)	(411)
Fair Value	268,696	302,234
CLO [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	361,323	425,083
Unrealized Gains	2,026	2,826
Unrealized Losses	(224)	(519)
Fair Value	363,125	427,390
Single issuer trust preferred securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	30,434	30,381
Unrealized Gains	891	0
Unrealized Losses	(123)	(1,748)
Fair Value	31,202	28,633
Corporate debt securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	107,228	108,490
Unrealized Gains	906	1,502
Unrealized Losses	(54)	(350)
Fair Value	108,080	109,642
Municipal bonds and notes [Member]
Held-to-maturity Securities [Abstract]
Amortized Cost	688,913	655,813
Unrealized Gains	5,111	4,389
Unrealized Losses	(14,605)	(25,749)
Fair Value	679,419	634,453
Private Label MBS [Member]
Held-to-maturity Securities [Abstract]
Amortized Cost	604	1,677
Unrealized Gains	3	12
Unrealized Losses	0	0
Fair Value	$ 607	$ 1,689

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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