Investment Securities (Schedule of Investment Securities Portfolio Continuous Unrealized Loss Position) (Detail) $ in Thousands	Sep. 30, 2022 USD ($)
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	$ 2,121,477
Continuous unrealized losses existing for less than 12 months, unrealized losses	(340,503)
Continuous unrealized losses existing for greater than 12 months, fair value	788,570
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(214,277)
Total, fair value	2,910,047
Total, unrealized losses	(554,780)
U.S. government agencies
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	44,013
Continuous unrealized losses existing for less than 12 months, unrealized losses	(5,987)
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	44,013
Total, unrealized losses	(5,987)
Municipal
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	128,642
Continuous unrealized losses existing for less than 12 months, unrealized losses	(5,960)
Continuous unrealized losses existing for greater than 12 months, fair value	31,753
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(1,778)
Total, fair value	160,395
Total, unrealized losses	(7,738)
Financial issuers
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	20,621
Continuous unrealized losses existing for less than 12 months, unrealized losses	(1,379)
Continuous unrealized losses existing for greater than 12 months, fair value	65,422
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(6,572)
Total, fair value	86,043
Total, unrealized losses	(7,951)
Other
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	990
Continuous unrealized losses existing for less than 12 months, unrealized losses	(10)
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	990
Total, unrealized losses	(10)
Mortgage-backed securities
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	1,847,405
Continuous unrealized losses existing for less than 12 months, unrealized losses	(308,051)
Continuous unrealized losses existing for greater than 12 months, fair value	691,395
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(205,927)
Total, fair value	2,538,800
Total, unrealized losses	(513,978)
Collateralized mortgage obligations
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	79,806
Continuous unrealized losses existing for less than 12 months, unrealized losses	(19,116)
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	79,806
Total, unrealized losses	$ (19,116)