Reserve for Known and Incurred but Not Reported Claims (Narrative) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reserve For Known And Incurred But Not Reported Claims [Line Items]
Payments, net of recoveries, related to: Current year	$ 242,617,000	$ 240,468,000	$ 223,735,000
Payments, net of recoveries, related to: Prior years	$ 208,139,000	$ 231,579,000	$ 239,264,000
Provision for title loss, percentage of title premiums and escrow fees	4.00%	4.00%	5.50%
Ultimate loss rate	4.00%	4.00%	4.50%
Estimated increase in loss reserve for prior policy years	$ 0	$ 0	$ 42,600,000
Ultimate loss in excess			$ 2,500,000
Projected ultimate loss ratio percentage	4.00%	3.90%	3.80%
Specialty Insurance
Reserve For Known And Incurred But Not Reported Claims [Line Items]
Payments, net of recoveries, related to: Current year	$ 228,300,000	$ 225,600,000	$ 211,300,000
Payments, net of recoveries, related to: Prior years	56,700,000	46,100,000	41,400,000
Property and Casualty Insurance Business
Reserve For Known And Incurred But Not Reported Claims [Line Items]
Payments on reinsured losses	15,300,000	8,900,000	2,100,000
Reinsurance recoveries	$ 20,300,000	$ 9,600,000	$ 2,000,000