Summary of Consolidated Investments-Other Than Investments in Related Parties (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Fixed Maturities
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fair Value	$ 3,082,923	[1]
Amortized Cost	3,125,413
Amount At Which Shown on Balance Sheet	3,082,923
Fixed Maturities | U.S. Treasury Bonds, Agency Bonds and Foreign Government Bonds
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fair Value	239,776	[1]
Amortized Cost	242,832
Amount At Which Shown on Balance Sheet	239,776
Fixed Maturities | States, Municipalities and Political Subdivisions
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fair Value	646,551	[1]
Amortized Cost	639,265
Amount At Which Shown on Balance Sheet	646,551
Fixed Maturities | Agency Residential Mortgage-Backed Securities
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fair Value	335,542	[1]
Amortized Cost	347,817
Amount At Which Shown on Balance Sheet	335,542
Fixed Maturities | Residential Mortgage Backed Securities
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fair Value	138,373	[1]
Amortized Cost	138,299
Amount At Which Shown on Balance Sheet	138,373
Fixed Maturities | Asset-Backed Securities
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fair Value	531,991	[1]
Amortized Cost	539,013
Amount At Which Shown on Balance Sheet	531,991
Fixed Maturities | Commercial Mortgage-Backed Securities
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fair Value	188,201	[1]
Amortized Cost	190,159
Amount At Which Shown on Balance Sheet	188,201
Fixed Maturities | Mortgage-Backed and Asset-Backed Securities
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fair Value	1,194,107	[1]
Amortized Cost	1,215,288
Amount At Which Shown on Balance Sheet	1,194,107
Fixed Maturities | Corporate Exposures
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fair Value	1,002,489	[1],[2]
Amortized Cost	1,028,028	[2]
Amount At Which Shown on Balance Sheet	1,002,489	[2]
Short-Term Investments
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fair Value	10,233	[1]
Amortized Cost	10,234
Amount At Which Shown on Balance Sheet	10,233
Equity Securities
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fair Value	339,892	[1]
Amortized Cost	361,418
Amount At Which Shown on Balance Sheet	339,892
Equity Securities | Common Stock
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fair Value	166,353	[1]
Amortized Cost	177,599
Amount At Which Shown on Balance Sheet	166,353
Equity Securities | Preferred Stocks
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fair Value	173,539	[1]
Amortized Cost	183,819
Amount At Which Shown on Balance Sheet	173,539
Investment Including Other Invested Assets
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fair Value	3,481,454	[1]
Amortized Cost	3,545,614
Amount At Which Shown on Balance Sheet	3,481,454
Other Invested Assets
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Fair Value	48,406	[1]
Amortized Cost	48,549
Amount At Which Shown on Balance Sheet	$ 48,406

[1] Other invested assets are accounted for using the equity method of accounting. All other investments are shown at fair value.

[2] Corporate Exposures consist of investments in corporate bonds, hybrid bonds and redeemable preferred stocks.