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		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Other Assets and Other Liabilities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		$ 35,666	$ 40,106	$ 43,234	$ 10,740
Total gains realized/unrealized:
Included in earnings	[1]	44,152	57,819	102,489	150,632
Transfers out of Level 3	[2]	(59,673)	(46,422)	(125,578)	(109,869)
Ending Balance		20,145	51,503	20,145	51,503
Changes in unrealized gains included in earnings related to assets still held at end of period	[1]	$ 18,196	44,127	21,722	50,411
Privately Issued [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance			16	16	16
Total gains realized/unrealized:
Settlements				$ (16)
Ending Balance			$ 16		$ 16

[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.