Investment Securities (Schedule of Investment Securities) (Detail) - USD ($)	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Available-for-sale securities
Amortized Cost	$ 3,193,741,000	$ 2,316,369,000	$ 2,395,927,000
Gross Unrealized Gains	1,978,000	40,094,000	61,967,000
Gross Unrealized Losses	(196,821,000)	(28,670,000)	(27,145,000)
Fair Value	2,998,898,000	2,327,793,000	2,430,749,000
Held-to-maturity securities
Amortized Cost	3,435,888,000	2,942,363,000	2,166,518,000
Gross Unrealized Gains	3,211,000	10,609,000	12,622,000
Gross Unrealized Losses	(292,672,000)	(52,278,000)	(58,075,000)
Fair Value	3,146,427,000	2,900,694,000	2,121,065,000
Less: Allowance for credit losses	(159,000)	(78,000)	(99,000)
Held-to-maturity securities, net of allowance for credit losses	3,435,729,000	2,942,285,000	2,166,419,000
Equity securities with readily determinable fair value
Amortized Cost	91,629,000	86,989,000	86,121,000
Gross Unrealized Gains	5,259,000	5,354,000	5,362,000
Gross Unrealized Losses	(4,199,000)	(1,832,000)	(1,145,000)
Fair Value	92,689,000	90,511,000	90,338,000
U.S. Treasury
Available-for-sale securities
Amortized Cost	0	0	64,999,000
Gross Unrealized Gains	0	0	2,000
Gross Unrealized Losses	0	0	0
Fair Value	0	0	65,001,000
U.S. Government agencies
Available-for-sale securities
Amortized Cost	50,000,000	50,158,000	77,908,000
Gross Unrealized Gains	366,000	2,349,000	3,618,000
Gross Unrealized Losses	(729,000)	0	0
Fair Value	49,637,000	52,507,000	81,526,000
Held-to-maturity securities
Amortized Cost	264,661,000	180,192,000	176,160,000
Gross Unrealized Gains	35,000	201,000	1,644,000
Gross Unrealized Losses	(27,673,000)	(3,314,000)	(7,230,000)
Fair Value	237,023,000	177,079,000	170,574,000
Municipal
Available-for-sale securities
Amortized Cost	157,563,000	161,618,000	143,711,000
Gross Unrealized Gains	1,019,000	4,193,000	4,761,000
Gross Unrealized Losses	(3,093,000)	(217,000)	(172,000)
Fair Value	155,489,000	165,594,000	148,300,000
Held-to-maturity securities
Amortized Cost	180,548,000	187,486,000	197,865,000
Gross Unrealized Gains	3,176,000	9,544,000	10,713,000
Gross Unrealized Losses	(1,693,000)	(223,000)	(535,000)
Fair Value	182,031,000	196,807,000	208,043,000
Corporate notes
Held-to-maturity securities
Amortized Cost	43,784,000	43,955,000	55,378,000
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	(3,205,000)	(1,119,000)	(1,196,000)
Fair Value	40,579,000	42,836,000	54,182,000
Financial issuers
Available-for-sale securities
Amortized Cost	86,994,000	96,878,000	91,806,000
Gross Unrealized Gains	1,000	418,000	461,000
Gross Unrealized Losses	(5,047,000)	(2,599,000)	(935,000)
Fair Value	81,948,000	94,697,000	91,332,000
Other
Available-for-sale securities
Amortized Cost	1,000,000	1,000,000	1,000,000
Gross Unrealized Gains	0	7,000	17,000
Gross Unrealized Losses	(9,000)	0	0
Fair Value	991,000	1,007,000	1,017,000
Mortgage-backed securities
Available-for-sale securities
Amortized Cost	2,794,760,000	1,901,005,000	2,007,092,000
Gross Unrealized Gains	591,000	32,830,000	52,855,000
Gross Unrealized Losses	(177,899,000)	(25,854,000)	(26,038,000)
Fair Value	2,617,452,000	1,907,981,000	2,033,909,000
Held-to-maturity securities
Amortized Cost	2,772,622,000	2,530,730,000	1,737,115,000
Gross Unrealized Gains	0	864,000	265,000
Gross Unrealized Losses	(253,254,000)	(47,622,000)	(49,114,000)
Fair Value	2,519,368,000	2,483,972,000	1,688,266,000
Collateralized mortgage obligations
Available-for-sale securities
Amortized Cost	103,424,000	105,710,000	9,411,000
Gross Unrealized Gains	1,000	297,000	253,000
Gross Unrealized Losses	(10,044,000)	0	0
Fair Value	93,381,000	106,007,000	9,664,000
Held-to-maturity securities
Amortized Cost	174,273,000	0	0
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	(6,847,000)	0	0
Fair Value	167,426,000	0	0
Mortgage-backed securities, subprime
Available-for-sale securities
Fair Value	$ 0	$ 0	$ 0