Schedule II - Condensed Financial Information Of The Registrant (Condensed Balance Sheets) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Fixed maturities - available for sale, at market value	$ 5,356,477	$ 5,293,411
Equity securities - available for sale, at fair value	1,215,377	1,299,037
Other invested assets	450,154	435,010
Other invested assets, at fair value	1,773,214	1,655,311
Short-term investments	563,536	564,364
Cash	155,429	323,975
Total investments and cash	9,516,289	9,572,633
Note receivable - affiliated	250,000	250,000
Accrued investment income	41,727	45,386
Other assets	261,805	235,576
TOTAL ASSETS	16,700,613	16,322,320
4.868% Senior notes due 6/1/2044	400,000	400,000
6.6% Long term notes due 05/01/2067	238,368	238,364
Accrued interest on debt and borrowings	3,537	3,537
Income taxes	68,024	46,835
Deferred tax liability	145,871	72,592
Other liabilities	249,658	361,874
Total liabilities	$ 11,769,402	$ 11,749,603
Common stock, par value: $0.01; 3,000 shares authorized; 1,000 shares issued and outstanding (2015 and 2014)
Additional paid-in capital	$ 374,789	$ 362,293
Accumulated other comprehensive income (loss), net deferred income tax expense (benefit)	(62,136)	4,519
Retained earnings	4,618,558	4,205,905
Total stockholder's equity	4,931,211	4,572,717	$ 4,190,478
TOTAL LIABILITIES AND STOCKHOLDER'S EQUITY	16,700,613	16,322,320
Fixed maturities - available for sale, at amortized cost	$ 5,335,472	$ 5,235,523
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	3,000	3,000
Common stock, shares issued	1,000	1,000
Common stock, shares outstanding	1,000	1,000
Accumulated other comprehensive income (loss), deferred income tax expense (benefit)	$ (33,458)	$ 2,434
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Fixed maturities - available for sale, at market value	65,441	9,040
Equity securities - available for sale, at fair value	131,219	96,890
Other invested assets	3,047	3,047
Other invested assets, at fair value	1,773,214	1,655,311
Short-term investments	37,802	92,390
Cash	6,232	6,206
Total investments and cash	2,016,955	1,862,884
Investment in subsidiaries, at equity in the underlying net assets	3,534,552	3,276,082
Note receivable - affiliated	250,000	250,000
Accrued investment income	438	92
Advances to affiliates	109,775	130,018
Other assets	18,097	18,340
TOTAL ASSETS	5,929,817	5,537,416
4.868% Senior notes due 6/1/2044	400,000	400,000
6.6% Long term notes due 05/01/2067	238,368	238,364
Accrued interest on debt and borrowings	3,537	3,537
Income taxes	354,312	317,991
Due to affiliates	1,049	932
Other liabilities	1,340	3,875
Total liabilities	$ 998,606	$ 964,699
Common stock, par value: $0.01; 3,000 shares authorized; 1,000 shares issued and outstanding (2015 and 2014)
Additional paid-in capital	$ 374,789	$ 362,293
Accumulated other comprehensive income (loss), net deferred income tax expense (benefit)	(62,136)	4,519
Retained earnings	4,618,558	4,205,905
Total stockholder's equity	4,931,211	4,572,717
TOTAL LIABILITIES AND STOCKHOLDER'S EQUITY	5,929,817	5,537,416
Fixed maturities - available for sale, at amortized cost	$ 66,016	$ 9,008
Debt instrument, interest rate, stated percentage	1.72%
Debt instrument, maturity date	Dec. 31, 2023
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	3,000,000	3,000,000
Common stock, shares issued	1,000,000	1,000,000
Common stock, shares outstanding	1,000,000	1,000,000
Accumulated other comprehensive income (loss), deferred income tax expense (benefit)	$ (33,458)	$ 2,434
Senior Notes [Member] | Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate, stated percentage	4.868%	4.868%
Debt instrument, maturity date	Jun. 01, 2044	Jun. 01, 2044
Long Term Subordinated Debt [Member]
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate, stated percentage	6.60%	6.60%
Debt instrument, maturity date	May 01, 2067
Long Term Subordinated Debt [Member] | Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Debt instrument, interest rate, stated percentage	6.60%	6.60%
Debt instrument, maturity date	May 01, 2067	May 01, 2067