Investment Securities (Schedule of Investment Securities) (Detail) - USD ($)	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022
Available-for-sale securities
Amortized Cost	$ 4,018,851,000	$ 3,769,634,000	$ 3,331,501,000
Gross Unrealized Gains	102,000	511,000	599,000
Gross Unrealized Losses	(526,472,000)	(527,128,000)	(361,979,000)
Fair Value	3,492,481,000	3,243,017,000	2,970,121,000
Held-to-maturity securities
Amortized Cost	3,564,879,000	3,641,055,000	3,413,552,000
Gross Unrealized Gains	397,000	477,000	1,197,000
Gross Unrealized Losses	(677,385,000)	(691,711,000)	(514,480,000)
Fair Value	2,887,891,000	2,949,821,000	2,900,269,000
Less: Allowance for credit losses	(406,000)	(488,000)	(83,000)
Held-to-maturity securities, net of allowance for credit losses	3,564,473,000	3,640,567,000	3,413,469,000
Equity securities with readily determinable fair value
Amortized Cost	120,629,000	115,552,000	96,247,000
Gross Unrealized Gains	3,711,000	2,935,000	3,143,000
Gross Unrealized Losses	(8,065,000)	(8,122,000)	(6,095,000)
Fair Value	116,275,000	110,365,000	93,295,000
U.S. Treasury
Available-for-sale securities
Amortized Cost	0	14,943,000	0
Gross Unrealized Gains	0	5,000	0
Gross Unrealized Losses	0	0	0
Fair Value	0	14,948,000	0
U.S. government agencies
Available-for-sale securities
Amortized Cost	80,000,000	80,000,000	50,000,000
Gross Unrealized Gains	0	36,000	0
Gross Unrealized Losses	(5,725,000)	(5,814,000)	(1,913,000)
Fair Value	74,275,000	74,222,000	48,087,000
Held-to-maturity securities
Amortized Cost	339,604,000	339,614,000	294,631,000
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	(71,022,000)	(75,293,000)	(53,222,000)
Fair Value	268,582,000	264,321,000	241,409,000
Municipal
Available-for-sale securities
Amortized Cost	173,540,000	173,861,000	170,268,000
Gross Unrealized Gains	102,000	230,000	570,000
Gross Unrealized Losses	(6,231,000)	(5,436,000)	(4,133,000)
Fair Value	167,411,000	168,655,000	166,705,000
Held-to-maturity securities
Amortized Cost	176,128,000	179,027,000	179,642,000
Gross Unrealized Gains	362,000	477,000	1,195,000
Gross Unrealized Losses	(4,502,000)	(4,066,000)	(2,796,000)
Fair Value	171,988,000	175,438,000	178,041,000
Corporate notes
Held-to-maturity securities
Amortized Cost	57,889,000	58,232,000	48,574,000
Gross Unrealized Gains	35,000	0	2,000
Gross Unrealized Losses	(4,733,000)	(5,348,000)	(4,158,000)
Fair Value	53,191,000	52,884,000	44,418,000
Financial issuers
Available-for-sale securities
Amortized Cost	83,995,000	93,994,000	93,994,000
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	(12,920,000)	(9,291,000)	(5,177,000)
Fair Value	71,075,000	84,703,000	88,817,000
Other
Available-for-sale securities
Amortized Cost	1,000,000	1,000,000	1,000,000
Gross Unrealized Gains	0	2,000	0
Gross Unrealized Losses	(15,000)	0	(4,000)
Fair Value	985,000	1,002,000	996,000
Mortgage-backed securities
Available-for-sale securities
Amortized Cost	3,585,943,000	3,308,494,000	2,915,107,000
Gross Unrealized Gains	0	238,000	28,000
Gross Unrealized Losses	(483,659,000)	(488,795,000)	(336,517,000)
Fair Value	3,102,284,000	2,819,937,000	2,578,618,000
Held-to-maturity securities
Amortized Cost	2,832,138,000	2,900,031,000	2,719,754,000
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	(574,114,000)	(583,682,000)	(438,050,000)
Fair Value	2,258,024,000	2,316,349,000	2,281,704,000
Collateralized mortgage obligations
Available-for-sale securities
Amortized Cost	94,373,000	97,342,000	101,132,000
Gross Unrealized Gains	0	0	1,000
Gross Unrealized Losses	(17,922,000)	(17,792,000)	(14,235,000)
Fair Value	76,451,000	79,550,000	86,898,000
Held-to-maturity securities
Amortized Cost	159,120,000	164,151,000	170,951,000
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	(23,014,000)	(23,322,000)	(16,254,000)
Fair Value	136,106,000	140,829,000	154,697,000
Mortgage-backed securities, subprime
Available-for-sale securities
Fair Value	$ 0	$ 0	$ 0