Schedule I Summary of Investments-Other Than Investments in Related Parties (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	$ 7,338,241	[1]
Total investments, Fair Value	0
Total investments, Amount shown in Balance Sheet	7,648,030
Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	6,785,626	[1]
Total investments, Fair Value	7,091,340
Total investments, Amount shown in Balance Sheet	7,091,340
Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	95,722	[1]
Total investments, Fair Value	99,797
Total investments, Amount shown in Balance Sheet	99,797
U.S. Government and federally sponsored agency obligations [Member] | Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	994,235	[1]
Total investments, Fair Value	1,050,525
Total investments, Amount shown in Balance Sheet	1,050,525
States, municipalities and political subdivisions [Member] | Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	1,553,603	[1]
Total investments, Fair Value	1,708,943
Total investments, Amount shown in Balance Sheet	1,708,943
Foreign government bonds [Member] | Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	67,441	[1]
Total investments, Fair Value	73,617
Total investments, Amount shown in Balance Sheet	73,617
Public utilities [Member] | Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	155,973	[1]
Total investments, Fair Value	174,831
Total investments, Amount shown in Balance Sheet	174,831
Other bonds [Member] | Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	4,014,374	[1]
Total investments, Fair Value	4,083,424
Total investments, Amount shown in Balance Sheet	4,083,424
Non-redeemable Preferred Stock [Member] | Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	16,268	[1]
Total investments, Fair Value	15,790
Total investments, Amount shown in Balance Sheet	15,790
Common Stocks [Member] | Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	59,450	[1]
Total investments, Fair Value	64,721
Total investments, Amount shown in Balance Sheet	64,721
Closed-end fund [Member] | Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	20,004	[1]
Total investments, Fair Value	19,286
Total investments, Amount shown in Balance Sheet	19,286
Short-term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	174,152	[1]
Total investments, Fair Value	0
Total investments, Amount shown in Balance Sheet	174,152
Policy Loans [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	148,696	[1]
Total investments, Fair Value	0
Total investments, Amount shown in Balance Sheet	148,696
Mortgages loan [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	63	[1]
Total investments, Fair Value	0
Total investments, Amount shown in Balance Sheet	63
Derivative instruments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	2,501	[1]
Total investments, Fair Value	0
Total investments, Amount shown in Balance Sheet	2,501
Other [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investments, Cost	131,481	[1]
Total investments, Fair Value	0
Total investments, Amount shown in Balance Sheet	$ 131,481

[1] Bonds at original cost reduced by repayments and adjusted for amortization of premiums or accrual of discounts and impairment in value of specifically identified investments.