Reserve for Known and Incurred but Not Reported Claims (Summary of Loss Reserves) (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Insurance [Abstract]
Known title claims, amount	$ 61.6	$ 55.5
Incurred but not reported claims, amount	1,162.5	1,186.5
Total title claims, amount	1,224.1	1,242.0
Non-title claims, amount	37.5	40.4
Total loss reserves, amount	$ 1,261.6	$ 1,282.4	$ 1,314.5	$ 1,325.3
Known title claims, percent	4.90%	4.30%
Incurred but not reported claims, percent	92.10%	92.50%
Total title claims, percent	97.00%	96.80%
Non-title claims, percent	3.00%	3.20%
Total loss reserves, percent	100.00%	100.00%