Summary Of Investments Other Than Investments In Related Parties (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	$ 1,433,330	[1]
Value	1,410,655
Amount Included in the Balance Sheet	1,410,655
Fixed Maturities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,257,830	[1]
Value	1,235,155
Amount Included in the Balance Sheet	1,235,155
Fixed Maturities | U.S. Treasury and Agency Obligations
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	79,766	[1]
Value	78,855
Amount Included in the Balance Sheet	78,855
Fixed Maturities | Obligations of States and Political Subdivisions
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	95,629	[1]
Value	95,613
Amount Included in the Balance Sheet	95,613
Fixed Maturities | Mortgage Backed And Asset Backed Securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	510,993	[1]
Value	504,330
Amount Included in the Balance Sheet	504,330
Fixed Maturities | Public Utility, Bonds
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	49,999	[1]
Value	49,608
Amount Included in the Balance Sheet	49,608
Fixed Maturities | All Other Corporate Bonds
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	521,443	[1]
Value	506,749
Amount Included in the Balance Sheet	506,749
Equity securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	124,747	[1]
Value	124,747
Amount Included in the Balance Sheet	124,747
Equity securities | Public Utility, Equities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	10,487	[1]
Value	10,487
Amount Included in the Balance Sheet	10,487
Equity securities | Industrial, Miscellaneous, and All Others
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	114,260	[1]
Value	114,260
Amount Included in the Balance Sheet	114,260
Other long-term investments | Other Invested Assets
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	50,753	[1]
Value	50,753
Amount Included in the Balance Sheet	$ 50,753

[1] Original cost of fixed maturities adjusted for amortization of premiums and accretion of discounts; original cost of equity securities and other long-term investments adjusted for income or loss earned on investments in accordance with equity method of accounting. All amounts are shown net of impairment losses.