Investment Securities Investment Securities (Narrative) (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Abstract]
Unrealized Losses	$ (13,223)	$ (98,669)
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Unrealized Losses	(13,551)	(128,201)
Debt Securities, Available-for-sale	2,960,103	2,898,730
Pledged Financial Instruments, Not Separately Reported, Securities	3,000,000	2,200,000
Agency CMO [Member]
Debt Securities, Available-for-sale [Abstract]
Unrealized Losses	(665)	(4,457)
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Unrealized Losses	(680)	(5,255)
Debt Securities, Available-for-sale	200,956	234,923
Agency MBS [Member]
Debt Securities, Available-for-sale [Abstract]
Unrealized Losses	(5,078)	(42,076)
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Unrealized Losses	(11,249)	(79,701)
Debt Securities, Available-for-sale	1,598,836	1,481,089
Agency CMBS [Member]
Debt Securities, Available-for-sale [Abstract]
Unrealized Losses	(2,814)	(41,930)
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Unrealized Losses	(1,569)	(22,572)
Debt Securities, Available-for-sale	610,350	566,237
Non-agency CMBS [Member]
Debt Securities, Available-for-sale [Abstract]
Unrealized Losses	(46)	(2,961)
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Unrealized Losses	(36)	(2,388)
Debt Securities, Available-for-sale	403,918	445,581
CLO [Member]
Debt Securities, Available-for-sale [Abstract]
Unrealized Losses	(367)	(1,964)
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Debt Securities, Available-for-sale	94,805	112,771
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Abstract]
Unrealized Losses	(4,253)	(5,281)
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Debt Securities, Available-for-sale	31,314	50,579
Municipal Bonds [Member]
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Unrealized Losses	(17)	$ (18,285)
Callable at the option of the counterparty [Member]
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Debt Securities, Available-for-sale	$ 1,300,000

Amount, before tax, of unrealized loss 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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Amount of 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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