Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Debt securities available for sale:
Due in one year or less	$ 3,470,536
Due after one year through five years	4,576,316
Due after five years through ten years	29,763
Due after ten years	30,000
Total available for sale (amortized cost)	8,106,615
Mortgage-backed securities available for sale	3,141,843
Investment securities available for sale, amortized cost	11,248,458	$ 11,248,458	$ 11,193,152
Debt securities held to maturity:
Due in one year or less	76,348
Due after one year through five years	1,132,418
Due after five years through ten years	1,191,409
Due after ten years	1,200,359
Total available for held to maturity (amortized cost)	3,600,534
Mortgage-backed securities held to maturity	12,317,572
Amortized cost for held to maturity	15,918,106		13,529,969
Debt securities available for sale:
Due in one year or less	3,391,769
Due after one year through five years	4,410,215
Due after five years through ten years	26,430
Due after ten years	24,254
Total available for sale (fair value)	7,852,668
Mortgage-backed securities available for sale	2,954,991
Total	10,807,659		10,748,961
Debt securities held to maturity:
Due in one year or less	76,153
Due after one year through five years	1,082,030
Due after five years through ten years	1,162,463
Due after ten years	1,130,162
Total available for held to maturity (fair value)	3,450,808
Mortgage-backed securities held to maturity	11,262,688
Total	$ 14,713,496	$ 14,713,496	$ 12,375,420