Reserve for Known and Incurred but Not Reported Claims (Summary of Loss Reserves) (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Insurance [Abstract]
Known title claims, amount	$ 67,487	$ 64,601
Incurred but not reported claims, amount	1,108,208	1,025,761
Total title claims, amount	1,175,695	1,090,362
Non-title claims, amount	85,820	87,642
Total loss reserves, amount	$ 1,261,515	$ 1,178,004	$ 1,069,859	$ 1,063,044
Known title claims, percent	5.40%	5.50%
Incurred but not reported claims, percent	87.80%	87.10%
Total title claims, percent	93.20%	92.60%
Non-title claims, percent	6.80%	7.40%
Total loss reserves, percent	100.00%	100.00%