Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Debt securities available for sale:
Due in one year or less	$ 6,912
Due after one year through five years	683,983
Due after five years through ten years	85,681
Due after ten years	30,000
Total available for sale (amortized cost)	806,576
Mortgage-backed securities available for sale	3,042,771
Investment securities available for sale, amortized cost	3,849,347	$ 4,621,027
Debt securities held to maturity:
Due in one year or less	3,229
Due after ten years	2,562
Total available for held to maturity (amortized cost)	5,791
Mortgage-backed securities held to maturity	2,728,883
Amortized cost for held to maturity	2,734,674	1,748,989
Debt securities available for sale:
Due in one year or less	6,943
Due after one year through five years	680,827
Due after five years through ten years	86,205
Due after ten years	26,517
Total available for sale (fair value)	800,492
Mortgage-backed securities available for sale	3,155,312
Total	3,955,804	4,822,606
Debt securities held to maturity:
Due in one year or less	3,222
Due after ten years	2,562
Total available for held to maturity (fair value)	5,784
Mortgage-backed securities held to maturity	2,765,506
Total	$ 2,771,290	$ 1,842,281