Investment Securities (Schedule of Investment Securities) (Detail) - USD ($)	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Available-for-sale securities
Amortized Cost	$ 3,331,501,000	$ 2,316,369,000	$ 2,148,058,000
Gross Unrealized Gains	599,000	40,094,000	59,364,000
Gross Unrealized Losses	(361,979,000)	(28,670,000)	(18,814,000)
Fair Value	2,970,121,000	2,327,793,000	2,188,608,000
Held-to-maturity securities
Amortized Cost	3,413,552,000	2,942,363,000	2,498,322,000
Gross Unrealized Gains	1,197,000	10,609,000	17,041,000
Gross Unrealized Losses	(514,480,000)	(52,278,000)	(35,131,000)
Fair Value	2,900,269,000	2,900,694,000	2,480,232,000
Less: Allowance for credit losses	(83,000)	(78,000)	(90,000)
Held-to-maturity securities, net of allowance for credit losses	3,413,469,000	2,942,285,000	2,498,232,000
Equity securities with readily determinable fair value
Amortized Cost	96,247,000	86,989,000	81,401,000
Gross Unrealized Gains	3,143,000	5,354,000	6,005,000
Gross Unrealized Losses	(6,095,000)	(1,832,000)	(1,090,000)
Fair Value	93,295,000	90,511,000	86,316,000
U.S. Treasury
Available-for-sale securities
Amortized Cost	0	0	0
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Fair Value	0	0	0
U.S. government agencies
Available-for-sale securities
Amortized Cost	50,000,000	50,158,000	75,169,000
Gross Unrealized Gains	0	2,349,000	3,685,000
Gross Unrealized Losses	(1,913,000)	0	0
Fair Value	48,087,000	52,507,000	78,854,000
Held-to-maturity securities
Amortized Cost	294,631,000	180,192,000	176,152,000
Gross Unrealized Gains	0	201,000	1,064,000
Gross Unrealized Losses	(53,222,000)	(3,314,000)	(3,454,000)
Fair Value	241,409,000	177,079,000	173,762,000
Municipal
Available-for-sale securities
Amortized Cost	170,268,000	161,618,000	163,715,000
Gross Unrealized Gains	570,000	4,193,000	4,738,000
Gross Unrealized Losses	(4,133,000)	(217,000)	(157,000)
Fair Value	166,705,000	165,594,000	168,296,000
Held-to-maturity securities
Amortized Cost	179,642,000	187,486,000	191,590,000
Gross Unrealized Gains	1,195,000	9,544,000	10,838,000
Gross Unrealized Losses	(2,796,000)	(223,000)	(308,000)
Fair Value	178,041,000	196,807,000	202,120,000
Corporate notes
Held-to-maturity securities
Amortized Cost	48,574,000	43,955,000	51,902,000
Gross Unrealized Gains	2,000	0	0
Gross Unrealized Losses	(4,158,000)	(1,119,000)	(535,000)
Fair Value	44,418,000	42,836,000	51,367,000
Financial issuers
Available-for-sale securities
Amortized Cost	93,994,000	96,878,000	98,827,000
Gross Unrealized Gains	0	418,000	520,000
Gross Unrealized Losses	(5,177,000)	(2,599,000)	(1,818,000)
Fair Value	88,817,000	94,697,000	97,529,000
Other
Available-for-sale securities
Amortized Cost	1,000,000	1,000,000	1,000,000
Gross Unrealized Gains	0	7,000	13,000
Gross Unrealized Losses	(4,000)	0	0
Fair Value	996,000	1,007,000	1,013,000
Mortgage-backed securities
Available-for-sale securities
Amortized Cost	2,915,107,000	1,901,005,000	1,800,751,000
Gross Unrealized Gains	28,000	32,830,000	50,171,000
Gross Unrealized Losses	(336,517,000)	(25,854,000)	(16,839,000)
Fair Value	2,578,618,000	1,907,981,000	1,834,083,000
Held-to-maturity securities
Amortized Cost	2,719,754,000	2,530,730,000	2,078,678,000
Gross Unrealized Gains	0	864,000	5,139,000
Gross Unrealized Losses	(438,050,000)	(47,622,000)	(30,834,000)
Fair Value	2,281,704,000	2,483,972,000	2,052,983,000
Collateralized mortgage obligations
Available-for-sale securities
Amortized Cost	101,132,000	105,710,000	8,596,000
Gross Unrealized Gains	1,000	297,000	237,000
Gross Unrealized Losses	(14,235,000)	0	0
Fair Value	86,898,000	106,007,000	8,833,000
Held-to-maturity securities
Amortized Cost	170,951,000	0	0
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	(16,254,000)	0	0
Fair Value	154,697,000	0	0
Mortgage-backed securities, subprime
Available-for-sale securities
Fair Value	$ 0	$ 0	$ 0