Investment Securities (Contractual Maturities of Investment Securities) (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Available-for-sale securities
Due in one year or less, amortized cost	$ 55,058	$ 49,714	$ 38,298
Due in one to five years, amortized cost	75,941	72,382	87,939
Due in five to ten years, amortized cost	115,378	118,358	119,858
Due after ten years, amortized cost	68,885	69,200	92,616
Amortized Cost	3,331,501	2,316,369	2,148,058
Due in one year or less, fair value	54,824	49,822	38,508
Due in one to five years, fair value	74,559	73,850	89,869
Due in five to ten years, fair value	109,492	117,573	119,979
Due after ten years, fair value	65,730	72,560	97,336
Fair Value	2,970,121	2,327,793	2,188,608
Held-to-maturity securities
Held-to-maturity securities, due in one year or less, amortized cost	1,457	2,976	5,119
Held-to-maturity securities, due in one to five years, amortized cost	84,906	79,422	56,059
Held-to-maturity securities, due in five to ten years, amortized cost	105,450	106,713	171,908
Held-to-maturity securities, due after ten years, amortized cost	331,034	222,522	186,558
Amortized Cost	3,413,552	2,942,363	2,498,322
Less: Allowance for credit losses	(83)	(78)	(90)
Held-to-maturity securities, net of allowance for credit losses	3,413,469	2,942,285	2,498,232
Held-to-maturity securities, due in one year or less, fair value	1,458	2,992	5,152
Held-to-maturity securities, due in one to five years, fair value	80,705	79,705	56,988
Held-to-maturity securities, due in five to ten years, fair value	105,491	112,667	178,864
Held-to-maturity securities, due after ten years, fair value	276,214	221,358	186,245
Fair Value	2,900,269	2,900,694	2,480,232
Mortgage-backed
Available-for-sale securities
Mortgage-backed, without single maturity date, amortized cost	3,016,239	2,006,715	1,809,347
Mortgage-backed, without single maturity date, fair value	2,665,516	2,013,988	1,842,916
Held-to-maturity securities
Mortgage-backed, amortized cost	2,890,705	2,530,730	2,078,678
Mortgage-backed, fair value	$ 2,436,401	$ 2,483,972	$ 2,052,983