Investment Securities (Summary Of Investment Securities) (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Available-for-sale Securities [Abstract]
Amortized Cost	$ 2,612,905	$ 3,015,763
Unrealized Gains	10,248	16,226
Unrealized Losses	(31,991)	(40,898)
Fair Value	2,591,162	2,991,091
Held-to-maturity Securities [Abstract]
Amortized Cost	4,497,311	4,160,658
Unrealized Gains	34,302	37,567
Unrealized Losses	(49,938)	(73,100)
Fair Value	4,481,675	4,125,125
US Treasury Bill Securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	3,596	734
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	3,596	734
Agency collateralized mortgage obligations (CMOs) [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	332,341	419,865
Unrealized Gains	2,573	3,344
Unrealized Losses	(3,116)	(3,503)
Fair Value	331,798	419,706
Held-to-maturity Securities [Abstract]
Amortized Cost	276,367	339,455
Unrealized Gains	1,138	1,977
Unrealized Losses	(3,030)	(3,824)
Fair Value	274,475	337,608
Agency mortgage-backed securities (MBS) [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	923,819	969,460
Unrealized Gains	3,214	4,398
Unrealized Losses	(14,056)	(19,509)
Fair Value	912,977	954,349
Held-to-maturity Securities [Abstract]
Amortized Cost	2,549,500	2,317,449
Unrealized Gains	24,275	26,388
Unrealized Losses	(30,012)	(41,768)
Fair Value	2,543,763	2,302,069
Agency commercial mortgage-backed securities (ACMBS) [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	599,165	587,776
Unrealized Gains	0	63
Unrealized Losses	(14,205)	(14,567)
Fair Value	584,960	573,272
Held-to-maturity Securities [Abstract]
Amortized Cost	708,229	547,726
Unrealized Gains	280	694
Unrealized Losses	(3,549)	(1,348)
Fair Value	704,960	547,072
Non-agency Commercial mortgage-backed securities (CMBS) [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	402,015	473,974
Unrealized Gains	1,539	4,093
Unrealized Losses	(121)	(702)
Fair Value	403,433	477,365
Held-to-maturity Securities [Abstract]
Amortized Cost	257,361	298,538
Unrealized Gains	3,394	4,107
Unrealized Losses	(197)	(411)
Fair Value	260,558	302,234
CLO [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	273,172	425,083
Unrealized Gains	1,572	2,826
Unrealized Losses	(161)	(519)
Fair Value	274,583	427,390
Single issuer trust preferred securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	30,463	30,381
Unrealized Gains	676	0
Unrealized Losses	(202)	(1,748)
Fair Value	30,937	28,633
Corporate debt securities [Member]
Available-for-sale Securities [Abstract]
Amortized Cost	48,334	108,490
Unrealized Gains	674	1,502
Unrealized Losses	(130)	(350)
Fair Value	48,878	109,642
Municipal bonds and notes [Member]
Held-to-maturity Securities [Abstract]
Amortized Cost	705,411	655,813
Unrealized Gains	5,213	4,389
Unrealized Losses	(13,150)	(25,749)
Fair Value	697,474	634,453
Private Label MBS [Member]
Held-to-maturity Securities [Abstract]
Amortized Cost	443	1,677
Unrealized Gains	2	12
Unrealized Losses	0	0
Fair Value	$ 445	$ 1,689

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

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