Investment Securities (Schedule of Investment Securities Portfolio Continuous Unrealized Loss Position) (Detail) - USD ($)	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	$ 318,267,000
Continuous unrealized losses existing for less than 12 months, unrealized losses	(8,325,000)
Continuous unrealized losses existing for greater than 12 months, fair value	2,549,590,000
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(474,037,000)
Total, fair value	2,867,857,000
Total, unrealized losses	(482,362,000)
Subprime mortgage-backed available-for-sale securities	3,259,845,000	$ 3,243,017,000	$ 2,998,898,000
U.S. government agencies
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	29,945,000
Continuous unrealized losses existing for less than 12 months, unrealized losses	(55,000)
Continuous unrealized losses existing for greater than 12 months, fair value	44,917,000
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(5,083,000)
Total, fair value	74,862,000
Total, unrealized losses	(5,138,000)
Subprime mortgage-backed available-for-sale securities	74,862,000	74,222,000	49,637,000
Municipal
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	58,695,000
Continuous unrealized losses existing for less than 12 months, unrealized losses	(624,000)
Continuous unrealized losses existing for greater than 12 months, fair value	55,413,000
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(3,539,000)
Total, fair value	114,108,000
Total, unrealized losses	(4,163,000)
Subprime mortgage-backed available-for-sale securities	160,386,000	168,655,000	155,489,000
Financial issuers
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	9,912,000
Continuous unrealized losses existing for less than 12 months, unrealized losses	(87,000)
Continuous unrealized losses existing for greater than 12 months, fair value	72,763,000
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(11,233,000)
Total, fair value	82,675,000
Total, unrealized losses	(11,320,000)
Subprime mortgage-backed available-for-sale securities	82,675,000	84,703,000	81,948,000
Mortgage-backed securities
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	219,643,000
Continuous unrealized losses existing for less than 12 months, unrealized losses	(7,558,000)
Continuous unrealized losses existing for greater than 12 months, fair value	2,297,025,000
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(437,847,000)
Total, fair value	2,516,668,000
Total, unrealized losses	(445,405,000)
Subprime mortgage-backed available-for-sale securities	2,856,430,000	2,819,937,000	2,617,452,000
Collateralized mortgage obligations
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	72,000
Continuous unrealized losses existing for less than 12 months, unrealized losses	(1,000)
Continuous unrealized losses existing for greater than 12 months, fair value	79,472,000
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(16,335,000)
Total, fair value	79,544,000
Total, unrealized losses	(16,336,000)
Subprime mortgage-backed available-for-sale securities	79,544,000	79,550,000	93,381,000
Mortgage-backed securities, subprime
Available-for-sale securities
Subprime mortgage-backed available-for-sale securities	$ 0	$ 0	$ 0