Investment Securities (Schedule of Investment Securities Portfolio Continuous Unrealized Loss Position) (Detail) - USD ($)	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	$ 1,008,946,000
Continuous unrealized losses existing for less than 12 months, unrealized losses	(20,549,000)
Continuous unrealized losses existing for greater than 12 months, fair value	2,471,210,000
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(505,923,000)
Total, fair value	3,480,156,000
Total, unrealized losses	(526,472,000)
Subprime mortgage-backed available-for-sale securities	3,492,481,000	$ 3,243,017,000	$ 2,970,121,000
U.S. government agencies
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	29,909,000
Continuous unrealized losses existing for less than 12 months, unrealized losses	(91,000)
Continuous unrealized losses existing for greater than 12 months, fair value	44,366,000
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(5,634,000)
Total, fair value	74,275,000
Total, unrealized losses	(5,725,000)
Subprime mortgage-backed available-for-sale securities	74,275,000	74,222,000	48,087,000
Municipal
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	101,356,000
Continuous unrealized losses existing for less than 12 months, unrealized losses	(1,988,000)
Continuous unrealized losses existing for greater than 12 months, fair value	53,731,000
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(4,243,000)
Total, fair value	155,087,000
Total, unrealized losses	(6,231,000)
Subprime mortgage-backed available-for-sale securities	167,411,000	168,655,000	166,705,000
Financial issuers
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	0
Continuous unrealized losses existing for less than 12 months, unrealized losses	0
Continuous unrealized losses existing for greater than 12 months, fair value	71,075,000
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(12,920,000)
Total, fair value	71,075,000
Total, unrealized losses	(12,920,000)
Subprime mortgage-backed available-for-sale securities	71,075,000	84,703,000	88,817,000
Other
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	985,000
Continuous unrealized losses existing for less than 12 months, unrealized losses	(15,000)
Continuous unrealized losses existing for greater than 12 months, fair value	0
Continuous unrealized losses existing for greater than 12 months, unrealized losses	0
Total, fair value	985,000
Total, unrealized losses	(15,000)
Subprime mortgage-backed available-for-sale securities	985,000	1,002,000	996,000
Mortgage-backed securities
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	876,659,000
Continuous unrealized losses existing for less than 12 months, unrealized losses	(18,454,000)
Continuous unrealized losses existing for greater than 12 months, fair value	2,225,624,000
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(465,205,000)
Total, fair value	3,102,283,000
Total, unrealized losses	(483,659,000)
Subprime mortgage-backed available-for-sale securities	3,102,284,000	2,819,937,000	2,578,618,000
Collateralized mortgage obligations
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	37,000
Continuous unrealized losses existing for less than 12 months, unrealized losses	(1,000)
Continuous unrealized losses existing for greater than 12 months, fair value	76,414,000
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(17,921,000)
Total, fair value	76,451,000
Total, unrealized losses	(17,922,000)
Subprime mortgage-backed available-for-sale securities	76,451,000	79,550,000	86,898,000
Mortgage-backed securities, subprime
Available-for-sale securities
Subprime mortgage-backed available-for-sale securities	$ 0	$ 0	$ 0