Investment Securities (Schedule of Investment Securities Portfolio Continuous Unrealized Loss Position) (Detail) $ in Thousands	Mar. 31, 2022 USD ($)
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	$ 2,296,022
Continuous unrealized losses existing for less than 12 months, unrealized losses	(128,973)
Continuous unrealized losses existing for greater than 12 months, fair value	543,886
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(67,848)
Total, fair value	2,839,908
Total, unrealized losses	(196,821)
U.S. Treasury
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	0
Continuous unrealized losses existing for greater than 12 months, unrealized losses	0
Total, fair value	0
Total, unrealized losses	0
U.S. Government agencies
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	9,271
Continuous unrealized losses existing for less than 12 months, unrealized losses	(729)
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	9,271
Total, unrealized losses	(729)
Municipal
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	92,896
Continuous unrealized losses existing for less than 12 months, unrealized losses	(2,861)
Continuous unrealized losses existing for greater than 12 months, fair value	3,553
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(232)
Total, fair value	96,449
Total, unrealized losses	(3,093)
Financial issuers
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	20,814
Continuous unrealized losses existing for less than 12 months, unrealized losses	(1,186)
Continuous unrealized losses existing for greater than 12 months, fair value	58,133
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(3,861)
Total, fair value	78,947
Total, unrealized losses	(5,047)
Other
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	991
Continuous unrealized losses existing for less than 12 months, unrealized losses	(9)
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	991
Total, unrealized losses	(9)
Mortgage-backed securities
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	2,078,794
Continuous unrealized losses existing for less than 12 months, unrealized losses	(114,144)
Continuous unrealized losses existing for greater than 12 months, fair value	482,200
Continuous unrealized losses existing for greater than 12 months, unrealized losses	(63,755)
Total, fair value	2,560,994
Total, unrealized losses	(177,899)
Collateralized mortgage obligations
Available-for-sale securities
Continuous unrealized losses existing for less than 12 months, fair value	93,256
Continuous unrealized losses existing for less than 12 months, unrealized losses	(10,044)
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	93,256
Total, unrealized losses	$ (10,044)