Investment Securities (Narrative) (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 13,852,000	$ 98,669,000
Held-to-maturity securities, accumulated unrealized holding loss	(16,421,000)	(128,201,000)
Investment securities available-for-sale, at fair value	2,925,833,000	2,898,730,000
Securities pledged to secure public funds, carrying value	2,700,000,000	2,200,000,000
Collateralized Mortgage Obligations [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	917,000	4,457,000
Held-to-maturity securities, accumulated unrealized holding loss	(1,200,000)	(5,255,000)
Investment securities available-for-sale, at fair value	185,801,000	234,923,000
Agency mortgage-backed securities (agency MBS) [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	4,035,000	42,076,000
Held-to-maturity securities, accumulated unrealized holding loss	(8,733,000)	(79,701,000)
Investment securities available-for-sale, at fair value	1,612,164,000	1,481,089,000
Agency commercial mortgage-backed securities (agency CMBS) [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	6,935,000	41,930,000
Held-to-maturity securities, accumulated unrealized holding loss	(5,615,000)	(22,572,000)
Investment securities available-for-sale, at fair value	581,552,000	566,237,000
Non-agency commercial mortgage-backed securities (non-agency CMBS) [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	252,000	2,961,000
Held-to-maturity securities, accumulated unrealized holding loss	(852,000)	(2,388,000)
Investment securities available-for-sale, at fair value	431,871,000	445,581,000
Collateralized loan obligations (CLO) [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	468,000	1,964,000
Investment securities available-for-sale, at fair value	92,205,000	112,771,000
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1,245,000	5,281,000
Investment securities available-for-sale, at fair value	22,240,000	50,579,000
Municipal bonds and notes [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities, accumulated unrealized holding loss	(21,000)	$ (18,285,000)
Callable at the option of the counterparty [Member]
Schedule of Investments [Line Items]
Investment securities available-for-sale, at fair value	$ 1,300,000,000