Investment Securities (Narrative) (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Investments [Line Items]
Gross unrealized losses	$ (40,898)	$ (33,290)
Available-for-sale securities, unrealized loss	40,898	33,290
Held-to-maturity securities, accumulated unrealized holding loss	(73,100)	(25,412)
Securities available-for-sale, at fair value	2,991,091	2,984,631
Securities pledged to secure public funds, carrying value	2,500,000	2,600,000
Agency collateralized mortgage obligations (agency CMO) [Member]
Schedule of Investments [Line Items]
Gross unrealized losses	(3,503)	(2,946)
Available-for-sale securities, unrealized loss	3,503	2,946
Held-to-maturity securities, accumulated unrealized holding loss	(3,824)	(2,058)
Securities available-for-sale, at fair value	419,706	548,754
Agency mortgage-backed securities (agency MBS) [Member]
Schedule of Investments [Line Items]
Gross unrealized losses	(19,509)	(17,291)
Available-for-sale securities, unrealized loss	19,509	17,291
Held-to-maturity securities, accumulated unrealized holding loss	(41,768)	(19,908)
Securities available-for-sale, at fair value	954,349	1,065,109
Agency commercial mortgage-backed securities (agency CMBS) [Member]
Schedule of Investments [Line Items]
Gross unrealized losses	(14,567)	(959)
Available-for-sale securities, unrealized loss	14,567	959
Held-to-maturity securities, accumulated unrealized holding loss	(1,348)	(325)
Securities available-for-sale, at fair value	573,272	215,350
Non-agency commercial mortgage-backed securities (non-agency CMBS) [Member]
Schedule of Investments [Line Items]
Gross unrealized losses	(702)	(2,905)
Available-for-sale securities, unrealized loss	702	2,905
Held-to-maturity securities, accumulated unrealized holding loss	(411)	(2,704)
Securities available-for-sale, at fair value	477,365	579,266
Collateralized loan obligations (CLO) [Member]
Schedule of Investments [Line Items]
Gross unrealized losses	(519)	(3,270)
Available-for-sale securities, unrealized loss	519	3,270
Securities available-for-sale, at fair value	427,390	429,159
Single issuer trust preferred securities [Member]
Schedule of Investments [Line Items]
Gross unrealized losses	(1,748)	(4,998)
Available-for-sale securities, unrealized loss	1,748	4,998
Securities available-for-sale, at fair value	28,633	37,170
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Gross unrealized losses	(350)	0
Available-for-sale securities, unrealized loss	350	0
Securities available-for-sale, at fair value	109,642	106,321
Municipal bonds and notes [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities, accumulated unrealized holding loss	(25,749)	$ (417)
Callable at the option of the counterparty [Member]
Schedule of Investments [Line Items]
Securities available-for-sale, at fair value	$ 1,900,000