Investment Securities (Summary Of Investment Securities) (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	$ 2,939,192	$ 2,994,616
Unrealized Gains	34,134	2,783
Unrealized Losses	(13,223)	(98,669)
Fair Value	2,960,103	2,898,730
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	5,193,521	4,325,420
Unrealized Gains	105,735	11,902
Unrealized Losses	(13,551)	(128,201)
Fair Value	5,285,705	4,209,121
US Treasury Bill Securities [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	19,918	7,549
Unrealized Gains	6	1
Unrealized Losses	0	0
Fair Value	19,924	7,550
Agency CMO [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	198,917	238,968
Unrealized Gains	2,704	412
Unrealized Losses	(665)	(4,457)
Fair Value	200,956	234,923
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	179,773	208,113
Unrealized Gains	1,430	287
Unrealized Losses	(680)	(5,255)
Fair Value	180,523	203,145
Agency MBS [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	1,573,984	1,521,534
Unrealized Gains	29,930	1,631
Unrealized Losses	(5,078)	(42,076)
Fair Value	1,598,836	1,481,089
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	3,085,000	2,517,823
Unrealized Gains	54,083	8,250
Unrealized Losses	(11,249)	(79,701)
Fair Value	3,127,834	2,446,372
Agency CMBS [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	611,925	608,167
Unrealized Gains	1,239	0
Unrealized Losses	(2,814)	(41,930)
Fair Value	610,350	566,237
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	950,217	667,500
Unrealized Gains	13,430	53
Unrealized Losses	(1,569)	(22,572)
Fair Value	962,078	644,981
Non-agency CMBS [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	403,782	447,897
Unrealized Gains	182	645
Unrealized Losses	(46)	(2,961)
Fair Value	403,918	445,581
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	235,687	216,943
Unrealized Gains	3,012	405
Unrealized Losses	(36)	(2,388)
Fair Value	238,663	214,960
CLO [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	95,099	114,641
Unrealized Gains	73	94
Unrealized Losses	(367)	(1,964)
Fair Value	94,805	112,771
Corporate debt securities [Member]
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	35,567	55,860
Unrealized Gains	0	0
Unrealized Losses	(4,253)	(5,281)
Fair Value	31,314	50,579
Municipal bonds and notes [Member]
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	742,844	715,041
Unrealized Gains	33,780	2,907
Unrealized Losses	(17)	(18,285)
Fair Value	$ 776,607	$ 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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