Investment Securities (Contractual Maturities of Investment Securities) (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Available-for-sale securities
Due in one year or less, amortized cost	$ 55,249	$ 49,714	$ 45,459
Due in one to five years, amortized cost	86,555	72,382	92,457
Due in five to ten years, amortized cost	115,949	118,358	121,099
Due after ten years, amortized cost	68,853	69,200	67,608
Amortized Cost	3,478,306	2,316,369	2,347,419
Due in one year or less, fair value	54,846	49,822	45,549
Due in one to five years, fair value	83,641	73,850	94,134
Due in five to ten years, fair value	105,921	117,573	121,650
Due after ten years, fair value	60,639	72,560	71,660
Fair Value	2,923,653	2,327,793	2,373,478
Held-to-maturity securities
Held-to-maturity securities, due in one year or less, amortized cost	1,173	2,976	5,466
Held-to-maturity securities, due in one to five years, amortized cost	85,423	79,422	75,724
Held-to-maturity securities, due in five to ten years, amortized cost	108,703	106,713	150,908
Held-to-maturity securities, due after ten years, amortized cost	348,026	222,522	186,398
Amortized Cost	3,390,152	2,942,363	2,736,805
Less: Allowance for credit losses	(310)	(78)	(83)
Held-to-maturity securities, net of allowance for credit losses	3,389,842	2,942,285	2,736,722
Held-to-maturity securities, due in one year or less, fair value	1,166	2,992	5,493
Held-to-maturity securities, due in one to five years, fair value	78,995	79,705	76,173
Held-to-maturity securities, due in five to ten years, fair value	104,829	112,667	157,282
Held-to-maturity securities, due after ten years, fair value	272,319	221,358	186,401
Fair Value	2,679,326	2,900,694	2,699,480
Mortgage-backed
Available-for-sale securities
Mortgage-backed, without single maturity date, amortized cost	3,151,700	2,006,715	2,020,796
Mortgage-backed, without single maturity date, fair value	2,618,606	2,013,988	2,040,485
Held-to-maturity securities
Mortgage-backed, amortized cost	2,846,827	2,530,730	2,318,309
Mortgage-backed, fair value	$ 2,222,017	$ 2,483,972	$ 2,274,131