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		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Other Assets and Other Liabilities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		$ 13,757	$ 35,027	$ 43,234	$ 10,740
Total gains realized/unrealized:
Included in earnings	[1]	52,312	48,732	58,337	92,813
Transfers out of Level 3	[2]	(30,403)	(43,653)	(65,905)	(63,447)
Ending Balance		35,666	40,106	35,666	40,106
Changes in unrealized gains included in earnings related to assets still held at end of period	[1]	37,300	33,725	35,492	38,514
Privately Issued [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		16	16	16	16
Total gains realized/unrealized:
Settlements		$ (16)		$ (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.