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	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Privately Issued Mortgage-Backed Securities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 16	$ 16	$ 22
Total gains realized/unrealized:
Settlements	(16)		(6)
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	7,712
Total gains realized/unrealized:
Included in earnings	126,223	194,469	129,398
Transfers out of Level 3	(163,017)	(161,975)	(126,370)
Ending Balance	6,440	43,234	10,740
Changes in unrealized gains included in earnings related to assets still held at end of period	$ 8,619	$ 42,597	$ 11,146