Fair Value Measurements - Changes in Level 3 Assets and Liabilities Measured at Estimated Fair Value on Recurring Basis (Detail) - Fair Value Measurements, Recurring [Member] - Significant Unobservable Inputs (Level 3) [Member] - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Privately Issued Mortgage-Backed Securities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		$ 16	$ 16
Total gains realized/unrealized:
Ending Balance		16	16
Other Assets and Other Liabilities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		43,234	10,740
Total gains realized/unrealized:
Included in earnings	[1]	6,025	44,081
Transfers out of Level 3	[2]	(35,502)	(19,794)
Ending Balance		13,757	35,027
Changes in unrealized gains included in earnings related to assets still held at end of period	[1]	$ 5,300	$ 32,584

[1] Reported as mortgage banking revenues in the consolidated statement of income and includes the fair value of commitment issuances and expirations

[2] Transfers out of Level 3 consist of interest rate locks transferred to closed loans.