Reserve for Known and Incurred but Not Reported Claims (Summary of Loss Reserves) (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Insurance [Abstract]
Known title claims, amount	$ 55.5	$ 62.1
IBNR title claims, amount	1,186.5	1,207.2
Total title claims, amount	1,242.0	1,269.3
Non-title claims, amount	40.4	56.0
Total loss reserves, amount	$ 1,282.4	$ 1,325.3	$ 1,283.8	$ 1,178.0
Known title claims, percent	4.30%	4.70%
IBNR title claims, percent	92.50%	91.10%
Total title claims, percent	96.80%	95.80%
Non-title claims, percent	3.20%	4.20%
Total loss reserves, percent	100.00%	100.00%