Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Debt securities available for sale:
Due in one year or less	$ 3,133,000
Due after one year through five years	4,789,000
Due after five years through ten years	0
Due after ten years	0
Total available for sale (amortized cost)	7,922,000
Mortgage-backed securities	6,209,000
Investment securities available for sale, amortized cost	14,131,000	$ 10,691,000
Debt securities held to maturity:
Due in one year or less	588,000
Due after one year through five years	653,000
Due after five years through ten years	1,392,000
Due after ten years	811,000
Total available for held to maturity (amortized cost)	3,444,000
Mortgage-backed securities	11,349,000
Amortized cost for held to maturity	14,793,000	15,330,000
Debt securities available for sale:
Due in one year or less	3,093,000
Due after one year through five years	4,744,000
Due after five years through ten years	0
Due after ten years	0
Total available for sale (fair value)	7,837,000
Mortgage-backed securities	6,055,000
Investment securities available for sale, estimated fair value	13,892,000	10,440,000
Debt securities held to maturity:
Due in one year or less	579,000
Due after one year through five years	628,000
Due after five years through ten years	1,332,000
Due after ten years	748,000
Total available for held to maturity (fair value)	3,287,000
Mortgage-backed securities	10,222,000
Estimated fair value for held to maturity	$ 13,509,000	$ 14,308,000