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

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity.

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This item represents an increase to the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held for which a previous OTTI was recognized and the investor does not intend to sell the debt security and it is not more likely than not that the investor will be required to sell the debt security before recovery of its amortized cost basis.

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Sum of the carrying amounts as of the date of the latest financial statement presented of securities which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Investment Securities (Narrative) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Schedule of Investments [Line Items]
Additions for OTTI not previously recognized in earnings	$ 0	$ 0	$ 126	$ 149
Available-for-sale - Accumulated Gross Unrealized Losses Before Tax	(31,991)		(31,991)		$ (40,898)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(49,938)		(49,938)		(73,100)
Investment securities available-for-sale, at fair value	2,591,162		2,591,162		2,991,091
Pledged Financial Instruments, Not Separately Reported, Securities	2,800,000		2,800,000		2,500,000
Agency collateralized mortgage obligations (CMOs) [Member]
Schedule of Investments [Line Items]
Available-for-sale - Accumulated Gross Unrealized Losses Before Tax	(3,116)		(3,116)		(3,503)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(3,030)		(3,030)		(3,824)
Investment securities available-for-sale, at fair value	331,798		331,798		419,706
Agency MBS [Member]
Schedule of Investments [Line Items]
Available-for-sale - Accumulated Gross Unrealized Losses Before Tax	(14,056)		(14,056)		(19,509)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(30,012)		(30,012)		(41,768)
Investment securities available-for-sale, at fair value	912,977		912,977		954,349
Agency CMBS [Member]
Schedule of Investments [Line Items]
Available-for-sale - Accumulated Gross Unrealized Losses Before Tax	(14,205)		(14,205)		(14,567)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(3,549)		(3,549)		(1,348)
Investment securities available-for-sale, at fair value	584,960		584,960		573,272
Non-agency Commercial mortgage-backed securities (CMBS) [Member]
Schedule of Investments [Line Items]
Available-for-sale - Accumulated Gross Unrealized Losses Before Tax	(121)		(121)		(702)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(197)		(197)		(411)
Investment securities available-for-sale, at fair value	403,433		403,433		477,365
CLO [Member]
Schedule of Investments [Line Items]
Available-for-sale - Accumulated Gross Unrealized Losses Before Tax	(161)		(161)		(519)
Investment securities available-for-sale, at fair value	274,583		274,583		427,390
Single issuer trust preferred securities [Member]
Schedule of Investments [Line Items]
Available-for-sale - Accumulated Gross Unrealized Losses Before Tax	(202)		(202)		(1,748)
Investment securities available-for-sale, at fair value	30,937		30,937		28,633
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale - Accumulated Gross Unrealized Losses Before Tax	(130)		(130)		(350)
Investment securities available-for-sale, at fair value	48,878		48,878		109,642
Municipal bonds and notes [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(13,150)		(13,150)		$ (25,749)
Callable at the option of the counterparty [Member]
Schedule of Investments [Line Items]
Investment securities available-for-sale, at fair value	$ 1,200,000		$ 1,200,000