Schedule II - Condensed Financial Information of Registrant (Statements of Cash Flows (Parent Company)) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Cash Flow Statements, Captions [Line Items]
Fixed maturity securities available for sale at fair value (cost $61,084 and $281,708 at December 31, 2013 and 2012, respectively)	$ 11,616,844	$ 11,943,956
Cash flows from operating activities:
Net income	499,925	510,592	391,211
Adjustments to reconcile net income to net cash from operating activities:
Net investment gains	(121,544)	(210,465)	(125,481)
Depreciation and amortization	103,090	103,419	88,012
Stock incentive plans	23,784	26,763	27,175
Change in:
Other liabilities	(2,826)	107,928	10,269
Net cash from operating activities	819,798	675,458	670,279
Cash from (used in) investing activities:
Proceeds from sale of fixed maturity securities	1,344,707	838,576	1,293,876
Proceeds from maturities and prepayments of fixed maturity securities	2,718,156	2,291,105	1,697,144
Proceeds from sales of equity securities	267,554	409,610	159,827
Cost of purchases of fixed maturity securities	(4,198,135)	(3,617,002)	(2,815,340)
Payments to Acquire Available-for-sale Securities, Equity	(156,557)	(284,991)	(97,986)
Change in balance due to security broker	(26,155)	(25,799)	(16,194)
Net additions to real estate, furniture & equipment	(63,150)	(40,556)	(45,320)
Net cash used investing activities	(545,364)	(775,068)	(204,274)
Cash from (used in) financing activities:
Net proceeds from stock options exercised	53	7,660	21,963
Purchase of common treasury shares	(166,473)	(127,663)	(187,163)
Cash dividends to common stockholders	(52,717)	(183,947)	(43,253)
Net cash from (used in) financing activities	(330,262)	97,192	(195,213)
Net increase (decrease) in cash and cash equivalents	(65,932)	(6,072)	268,790
Cash and cash equivalents at beginning of year	905,670	911,742	642,952
Cash and cash equivalents at end of year	839,738	905,670	911,742
Parent Company
Condensed Cash Flow Statements, Captions [Line Items]
Fixed maturity securities available for sale at fair value (cost $61,084 and $281,708 at December 31, 2013 and 2012, respectively)	63,115	286,597
Cash flows from operating activities:
Net income	499,925	510,592	391,211
Adjustments to reconcile net income to net cash from operating activities:
Net investment gains	(24,550)	(71,130)	(45,962)
Depreciation and amortization	10,397	5,624	4,905
Equity in undistributed earnings of subsidiaries	(369,640)	(694,701)	(71,146)
Tax payments received from subsidiaries	77,305	125,046	139,011
Federal income taxes provided by subsidiaries on a separate return basis	(225,845)	(132,379)	(79,200)
Stock incentive plans	24,594	26,763	27,176
Change in:
Federal income taxes	21,866	44,423	56,542
Other assets	(821)	911	(542)
Other liabilities	(16,280)	28,017	(6,747)
Accrued investment income	967	97	1,559
Other, net	0	(13)	277
Net cash from operating activities	(2,082)	(156,750)	417,084
Cash from (used in) investing activities:
Proceeds from sale of fixed maturity securities	230,854	93,354	70,665
Proceeds from maturities and prepayments of fixed maturity securities	68,918	121,191	165,158
Proceeds from sales of equity securities	23,395	72,565	47,735
Cost of purchases of fixed maturity securities	(79,132)	(255,885)	(240,536)
Payments to Acquire Available-for-sale Securities, Equity	(4,668)	0	0
Investments in and advances to subsidiaries, net	(58,454)	(16,480)	(3,867)
Change in balance due to security broker	6,918	(4,767)	(5,983)
Net additions to real estate, furniture & equipment	(1,896)	(1,857)	(643)
Net cash used investing activities	185,935	8,121	32,529
Cash from (used in) financing activities:
Net proceeds from issuance of senior notes	339,627	345,823	0
Net proceeds from stock options exercised	53	13,544	21,966
Repayment of senior notes	(450,000)	0	0
Purchase of common treasury shares	(166,473)	(134,456)	(187,163)
Cash dividends to common stockholders	(52,717)	(183,947)	(43,255)
Net cash from (used in) financing activities	(329,510)	40,964	(208,452)
Net increase (decrease) in cash and cash equivalents	(145,657)	(107,665)	241,161
Cash and cash equivalents at beginning of year	162,972	270,637	29,476
Cash and cash equivalents at end of year	$ 17,315	$ 162,972	$ 270,637