Accumulated Other Comprehensive Income (Loss) (Reclassifications Out of AOCI) (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Credit losses recognized on debt securities				$ (195)
Pretax total		$ 827	$ (144)	(2,538)	$ (82)
Amortization of net actuarial loss				(2,640)
Amortization of prior service credit				1,554
Unrealized Gains (Losses) on Debt Securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) on sales of debt securities		1,384	(246)	6,055	(287)
Credit losses recognized on debt securities		(14)		(7,507)
Pretax total		1,370	(246)	(1,452)	(287)
Tax effect		(322)	58	360	68
Pension Benefit Adjustment Attributable to First American Financial Corporation
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Pretax total	[1]	(543)	102	(1,086)	205
Tax effect	[1]	144	(27)	288	(54)
Amortization of net actuarial loss	[1]	(1,320)	(915)	(2,640)	(1,830)
Amortization of prior service credit	[1]	$ 777	$ 1,017	$ 1,554	$ 2,035

[1] These components of AOCI are components of net periodic cost.  See Note 11 Employee Benefit Plans for additional details