Investment Securities (Schedule of Investment Securities) (Detail) - USD ($)	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Available-for-sale securities
Amortized Cost	$ 3,739,980,000	$ 3,769,634,000	$ 3,193,741,000
Gross Unrealized Gains	2,227,000	511,000	1,978,000
Gross Unrealized Losses	(482,362,000)	(527,128,000)	(196,821,000)
Fair Value	3,259,845,000	3,243,017,000	2,998,898,000
Held-to-maturity securities
Amortized Cost	3,606,854,000	3,641,055,000	3,435,888,000
Gross Unrealized Gains	2,352,000	477,000	3,211,000
Gross Unrealized Losses	(633,008,000)	(691,711,000)	(292,672,000)
Fair Value	2,976,198,000	2,949,821,000	3,146,427,000
Less: Allowance for credit losses	(463,000)	(488,000)	(159,000)
Held-to-maturity securities, net of allowance for credit losses	3,606,391,000	3,640,567,000	3,435,729,000
Equity securities with readily determinable fair value
Amortized Cost	116,296,000	115,552,000	91,629,000
Gross Unrealized Gains	3,065,000	2,935,000	5,259,000
Gross Unrealized Losses	(7,418,000)	(8,122,000)	(4,199,000)
Fair Value	111,943,000	110,365,000	92,689,000
U.S. Treasury
Available-for-sale securities
Amortized Cost	4,947,000	14,943,000	0
Gross Unrealized Gains	1,000	5,000	0
Gross Unrealized Losses	0	0	0
Fair Value	4,948,000	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	366,000
Gross Unrealized Losses	(5,138,000)	(5,814,000)	(729,000)
Fair Value	74,862,000	74,222,000	49,637,000
Held-to-maturity securities
Amortized Cost	339,608,000	339,614,000	264,661,000
Gross Unrealized Gains	24,000	0	35,000
Gross Unrealized Losses	(70,064,000)	(75,293,000)	(27,673,000)
Fair Value	269,568,000	264,321,000	237,023,000
Municipal
Available-for-sale securities
Amortized Cost	164,110,000	173,861,000	157,563,000
Gross Unrealized Gains	439,000	230,000	1,019,000
Gross Unrealized Losses	(4,163,000)	(5,436,000)	(3,093,000)
Fair Value	160,386,000	168,655,000	155,489,000
Held-to-maturity securities
Amortized Cost	174,720,000	179,027,000	180,548,000
Gross Unrealized Gains	1,117,000	477,000	3,176,000
Gross Unrealized Losses	(2,880,000)	(4,066,000)	(1,693,000)
Fair Value	172,957,000	175,438,000	182,031,000
Corporate notes
Held-to-maturity securities
Amortized Cost	58,061,000	58,232,000	43,784,000
Gross Unrealized Gains	14,000	0	0
Gross Unrealized Losses	(4,218,000)	(5,348,000)	(3,205,000)
Fair Value	53,857,000	52,884,000	40,579,000
Financial issuers
Available-for-sale securities
Amortized Cost	93,995,000	93,994,000	86,994,000
Gross Unrealized Gains	0	0	1,000
Gross Unrealized Losses	(11,320,000)	(9,291,000)	(5,047,000)
Fair Value	82,675,000	84,703,000	81,948,000
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	0	0	(9,000)
Fair Value	1,000,000	1,002,000	991,000
Mortgage-backed securities
Available-for-sale securities
Amortized Cost	3,300,048,000	3,308,494,000	2,794,760,000
Gross Unrealized Gains	1,787,000	238,000	591,000
Gross Unrealized Losses	(445,405,000)	(488,795,000)	(177,899,000)
Fair Value	2,856,430,000	2,819,937,000	2,617,452,000
Held-to-maturity securities
Amortized Cost	2,872,591,000	2,900,031,000	2,772,622,000
Gross Unrealized Gains	1,197,000	0	0
Gross Unrealized Losses	(533,415,000)	(583,682,000)	(253,254,000)
Fair Value	2,340,373,000	2,316,349,000	2,519,368,000
Collateralized mortgage obligations
Available-for-sale securities
Amortized Cost	95,880,000	97,342,000	103,424,000
Gross Unrealized Gains	0	0	1,000
Gross Unrealized Losses	(16,336,000)	(17,792,000)	(10,044,000)
Fair Value	79,544,000	79,550,000	93,381,000
Held-to-maturity securities
Amortized Cost	161,874,000	164,151,000	174,273,000
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	(22,431,000)	(23,322,000)	(6,847,000)
Fair Value	139,443,000	140,829,000	167,426,000
Mortgage-backed securities, subprime
Available-for-sale securities
Fair Value	$ 0	$ 0	$ 0