Investment Securities (Summary Of Investment Securities) (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	$ 2,990,650	$ 2,994,616
Unrealized Gains	22,199	2,783
Unrealized Losses	(34,192)	(98,669)
Fair Value	2,978,657	2,898,730
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	4,636,707	4,325,420
Unrealized Gains	64,197	11,902
Unrealized Losses	(26,394)	(128,201)
Fair Value	4,674,510	4,209,121
US Treasury Bill Securities [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	9,997	7,549
Unrealized Gains	1	1
Unrealized Losses	0	0
Fair Value	9,998	7,550
Agency CMO [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	213,307	238,968
Unrealized Gains	2,209	412
Unrealized Losses	(1,264)	(4,457)
Fair Value	214,252	234,923
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	190,858	208,113
Unrealized Gains	1,089	287
Unrealized Losses	(1,406)	(5,255)
Fair Value	190,541	203,145
Agency MBS [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	1,612,028	1,521,534
Unrealized Gains	19,109	1,631
Unrealized Losses	(11,665)	(42,076)
Fair Value	1,619,472	1,481,089
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	2,736,676	2,517,823
Unrealized Gains	33,098	8,250
Unrealized Losses	(20,616)	(79,701)
Fair Value	2,749,158	2,446,372
Agency CMBS [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	594,548	608,167
Unrealized Gains	175	0
Unrealized Losses	(16,022)	(41,930)
Fair Value	578,701	566,237
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	768,076	667,500
Unrealized Gains	3,988	53
Unrealized Losses	(3,684)	(22,572)
Fair Value	768,380	644,981
Non-agency CMBS [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	428,492	447,897
Unrealized Gains	599	645
Unrealized Losses	(23)	(2,961)
Fair Value	429,068	445,581
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	194,752	216,943
Unrealized Gains	2,549	405
Unrealized Losses	(37)	(2,388)
Fair Value	197,264	214,960
CLO [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	96,727	114,641
Unrealized Gains	106	94
Unrealized Losses	(444)	(1,964)
Fair Value	96,389	112,771
Corporate debt securities [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	35,551	55,860
Unrealized Gains	0	0
Unrealized Losses	(4,774)	(5,281)
Fair Value	30,777	50,579
Municipal bonds and notes [Member]
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	746,345	715,041
Unrealized Gains	23,473	2,907
Unrealized Losses	(651)	(18,285)
Fair Value	$ 769,167	$ 699,663

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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