Investment Securities (Contractual Maturities of Investment Securities) (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Available-for-sale securities
Due in one year or less, amortized cost	$ 108,880	$ 119,830	$ 48,130
Due in one to five years, amortized cost	131,959	63,644	67,138
Due in five to ten years, amortized cost	39,019	115,734	110,960
Due after ten years, amortized cost	64,194	64,590	69,329
Amortized Cost	3,739,980	3,769,634	3,193,741
Due in one year or less, fair value	108,429	119,275	47,945
Due in one to five years, fair value	122,172	61,701	66,034
Due in five to ten years, fair value	35,158	105,076	105,670
Due after ten years, fair value	58,112	57,478	68,416
Fair Value	3,259,845	3,243,017	2,998,898
Held-to-maturity securities
Held-to-maturity securities, due in one year or less, amortized cost	2,302	1,340	1,208
Held-to-maturity securities, due in one to five years, amortized cost	98,207	94,705	83,085
Held-to-maturity securities, due in five to ten years, amortized cost	110,967	115,318	101,410
Held-to-maturity securities, due after ten years, amortized cost	360,913	365,510	303,290
Amortized Cost	3,606,854	3,641,055	3,435,888
Less: Allowance for credit losses	(463)	(488)	(159)
Held-to-maturity securities, net of allowance for credit losses	3,606,391	3,640,567	3,435,729
Held-to-maturity securities, due in one year or less, fair value	2,300	1,332	1,213
Held-to-maturity securities, due in one to five years, fair value	93,717	89,093	80,210
Held-to-maturity securities, due in five to ten years, fair value	110,892	113,758	102,940
Held-to-maturity securities, due after ten years, fair value	289,473	288,460	275,270
Fair Value	2,976,198	2,949,821	3,146,427
Mortgage-backed
Available-for-sale securities
Mortgage-backed, without single maturity date, amortized cost	3,395,928	3,405,836	2,898,184
Mortgage-backed, without single maturity date, fair value	2,935,974	2,899,487	2,710,833
Held-to-maturity securities
Mortgage-backed, amortized cost	3,034,465	3,064,182	2,946,895
Mortgage-backed, fair value	$ 2,479,816	$ 2,457,178	$ 2,686,794