Reserve for Known and Incurred but Not Reported Claims (Summary of Loss Reserves) (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Insurance [Abstract]
Known title claims, amount	$ 81,212	$ 83,094
Incurred but not reported claims, amount	881,071	875,724
Total title claims, amount	962,283	958,818
Non-title claims, amount	64,676	70,115
Total loss reserves, amount	$ 1,026,959	$ 1,028,933	$ 1,021,648	$ 1,025,863
Known title claims, percent	7.90%	8.10%
Incurred but not reported claims, percent	85.80%	85.10%
Total title claims, percent	93.70%	93.20%
Non-title claims, percent	6.30%	6.80%
Total loss reserves, percent	100.00%	100.00%