Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt securities available for sale:
Due in one year or less	$ 4,619,339
Due after one year through five years	3,437,580
Due after five years through ten years	24,974
Due after ten years	30,000
Total available for sale (amortized cost)	8,111,893
Mortgage-backed securities available for sale	2,927,073
Investment securities available for sale, amortized cost	11,038,966	$ 11,193,152
Debt securities held to maturity:
Due in one year or less	14,164
Due after one year through five years	1,151,126
Due after five years through ten years	1,306,208
Due after ten years	1,043,889
Total available for held to maturity (amortized cost)	3,515,387
Mortgage-backed securities held to maturity	12,055,733
Amortized cost for held to maturity	15,571,120	13,529,969
Debt securities available for sale:
Due in one year or less	4,544,581
Due after one year through five years	3,306,540
Due after five years through ten years	22,400
Due after ten years	25,132
Total available for sale (fair value)	7,898,653
Mortgage-backed securities available for sale	2,693,756
Total	10,592,409	10,748,961
Debt securities held to maturity:
Due in one year or less	13,967
Due after one year through five years	1,097,310
Due after five years through ten years	1,223,790
Due after ten years	912,465
Total available for held to maturity (fair value)	3,247,532
Mortgage-backed securities held to maturity	10,517,411
Total	$ 13,764,943	$ 12,375,420