Reserve for Known and Incurred but Not Reported Claims (Narrative) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reserve For Known And Incurred But Not Reported Claims [Line Items]
Payments, net of recoveries, related to: Current year	$ 227,663,000	$ 242,617,000	$ 240,468,000
Payments, net of recoveries, related to: Prior years	187,658,000	$ 208,139,000	$ 231,579,000
Payments on reinsured losses	$ 5,991,000
Provision for title loss, percentage of title premiums and escrow fees	4.00%	4.00%	4.00%
Ultimate loss rate	4.00%	4.00%	4.00%
Estimated increase in loss reserve for prior policy years	$ 0	$ 0	$ 0
Specialty Insurance
Reserve For Known And Incurred But Not Reported Claims [Line Items]
Payments, net of recoveries, related to: Current year	211,400,000	228,300,000	225,600,000
Payments, net of recoveries, related to: Prior years	41,700,000	56,700,000	46,100,000
Property and Casualty Insurance Business
Reserve For Known And Incurred But Not Reported Claims [Line Items]
Payments on reinsured losses	21,100,000	15,300,000	8,900,000
Reinsurance recoveries	$ 10,300,000	$ 20,300,000	$ 9,600,000