Reserve for Known and Incurred but Not Reported Claims (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Insurance [Abstract]
Provision for title loss, percentage of title premiums and escrow fees	4.00%	5.00%	4.00%	5.00%
Ultimate loss rate		5.00%	4.00%		4.50%
Estimated increase in loss reserve for prior policy years	$ 0.0	$ 7.0		$ 18.2
Percentage Increase In Loss Reserve Estimates For Prior Policy Years		0.50%		0.50%