SCHEDULE II-CONDENSED FINANCIAL INFORMATION OF REGISTRANT (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Mar. 31, 2013	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jun. 30, 2013
ASSETS
Fixed maturities (amortized cost, 2015 – $385,281; 2014 – $482,629)													$ 4,657,561	$ 4,609,614
Cash and cash equivalents		$ 181,120			$ 197,882	$ 197,882			$ 332,692	$ 197,882	$ 332,692	$ 1,027,625	181,120	197,882	$ 332,692
Accrued investment income													40,224	30,518
Other assets													91,138	106,390
Total assets													5,879,545	5,266,434
Liabilities:
Senior notes													0	61,918
Convertible senior notes													833,503	845,000
Convertible junior debentures													389,522	389,522
Total liabilities													3,643,405	4,229,531
Shareholders’ equity:
Common stock (one dollar par value, shares authorized 1,000,000; shares issued 2015 - 340,097; 2014 - 340,047; outstanding 2015 - 339,657; 2014 - 338,560)													340,097	340,047
Paid-in capital													1,670,238	1,663,592
Treasury stock (shares at cost, 2015 – 440; 2014 – 1,487)													(3,362)	(32,937)
Accumulated other comprehensive loss, net of tax													(60,880)	(81,341)
Retained earnings (deficit)													290,047	(852,458)
Total shareholders' equity													2,236,140	1,036,903	744,538
Total liabilities and shareholders' equity													5,879,545	5,266,434
Parenthetical information [Abstract]
Fixed maturities, amortized cost													$ 4,684,148	$ 4,602,514
Common stock, par value (in dollars per share)													$ 1	$ 1
Common stock, shares authorized (in shares)													1,000,000,000	1,000,000,000		680,000,000
Common stock, shares issued (in shares)													340,097,000	340,047,000
Common stock, shares outstanding (in shares)													339,657,000	338,560,000
Treasury stock, shares at cost (in shares)													440,000	1,487,000
Revenues:
Investment income, net of expenses		27,926	$ 25,939	$ 25,756	24,120	23,956	$ 22,355	$ 21,180	20,156	103,741	87,647	80,739
Realized (losses) gains		1,228	640	166	26,327	434	632	522	(231)	28,361	1,357	5,731
Total revenues										1,040,781	941,797	1,039,435
Expenses:
Interest expense										68,932	69,648	79,663
Total losses and expenses										553,094	687,074	1,085,587
Income (loss) before tax										487,687	254,723	(46,152)
(Benefit from) provision for income tax		6,584	(695,604)	1,322	3,385	681	249	1,118	726	(684,313)	2,774	3,696
Net income (loss)		102,418	822,852	113,654	133,076	74,428	72,017	45,522	59,982	1,172,000	251,949	(49,848)
Other comprehensive income (loss), net of tax										20,461	36,385	(69,563)
Comprehensive income (loss)										1,192,461	288,334	(119,411)
Cash flows from operating activities:
Net income (loss)		102,418	$ 822,852	$ 113,654	133,076	74,428	$ 72,017	$ 45,522	59,982	1,172,000	251,949	(49,848)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Deferred Federal										(686,652)	1	7
Change in certain assets and liabilities:
Accrued investment income										(9,706)	1,142	(4,417)
Cash flows from investing activities:
Purchase of fixed maturities										(2,462,844)	(1,979,917)	(3,248,602)
Sale of fixed maturities										1,796,153	1,147,624	1,054,985
Cash flows from financing activities:
Net proceeds from convertible senior notes										0	0	484,625
Common stock shares issued	$ 663,300									0	0	663,335
Excess tax benefits related to share-based compensation										2,117	0	0
Net decrease in cash and cash equivalents										(16,762)	(134,810)	(694,933)
Cash and cash equivalents at beginning of year					197,882				332,692	197,882	332,692	1,027,625
Cash and cash equivalents at end of year		181,120				197,882				181,120	197,882	332,692
Parent Company
ASSETS
Fixed maturities (amortized cost, 2015 – $385,281; 2014 – $482,629)													$ 382,565	$ 480,125
Cash and cash equivalents		19,417			10,507	10,507			20,725	10,507	20,725	175,880	19,417	10,507	$ 20,725
Investment in subsidiaries, at equity in net assets													2,903,944	1,821,024
Accounts receivable - affiliates													938	312
Income taxes - current and deferred													151,318	17,478
Accrued investment income													3,700	3,435
Other assets													11,325	15,156
Total assets													3,473,207	2,348,037
Liabilities:
Senior notes													0	61,918
Convertible senior notes													833,503	845,000
Convertible junior debentures													389,522	389,522
Accrued interest													14,042	14,694
Total liabilities													1,237,067	1,311,134
Shareholders’ equity:
Common stock (one dollar par value, shares authorized 1,000,000; shares issued 2015 - 340,097; 2014 - 340,047; outstanding 2015 - 339,657; 2014 - 338,560)													340,097	340,047
Paid-in capital													1,670,238	1,663,592
Treasury stock (shares at cost, 2015 – 440; 2014 – 1,487)													(3,362)	(32,937)
Accumulated other comprehensive loss, net of tax													(60,880)	(81,341)
Retained earnings (deficit)													290,047	(852,458)
Total shareholders' equity													2,236,140	1,036,903
Total liabilities and shareholders' equity													3,473,207	2,348,037
Parenthetical information [Abstract]
Fixed maturities, amortized cost													$ 385,281	$ 482,629
Common stock, par value (in dollars per share)													$ 1	$ 1
Common stock, shares authorized (in shares)													1,000,000,000	1,000,000,000
Common stock, shares issued (in shares)													340,097,000	340,047,000
Common stock, shares outstanding (in shares)													339,657,000	338,560,000
Treasury stock, shares at cost (in shares)													440,000	1,487,000
Revenues:
Investment income, net of expenses										7,586	6,985	5,033
Realized (losses) gains										357	395	830
Total revenues										7,943	7,380	5,863
Expenses:
Operating expenses and other										1,089	1,383	511
Interest expense										68,932	69,648	79,663
Total losses and expenses										70,021	71,031	80,174
Income (loss) before tax										(62,078)	(63,651)	(74,311)
(Benefit from) provision for income tax										(125,487)	0	0
Equity in net income of subsidiaries										1,108,591	315,600	24,463
Net income (loss)										1,172,000	251,949	(49,848)
Other comprehensive income (loss), net of tax										20,461	36,385	(69,563)
Comprehensive income (loss)										1,192,461	288,334	(119,411)
Cash flows from operating activities:
Net income (loss)										1,172,000	251,949	(49,848)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Equity in net income of subsidiaries										(1,108,591)	(315,600)	(24,463)
Dividends received from subsidiaries										6,500	0	0
Deferred Federal										(125,532)	0	0
Other										22,849	14,862	21,693
Change in certain assets and liabilities:
Accounts receivable - affiliates										(626)	68	289
Income taxes receivable										(8,308)	480	(3)
Accrued investment income										(265)	194	(2,611)
Accrued interest										(652)	(188)	(15,577)
Net cash used in operating activities										(42,625)	(48,235)	(70,520)
Cash flows from investing activities:
Capital distributions from (contributions to) subsidiaries										32,000	0	(800,000)
Purchase of fixed maturities										(295,010)	(553,538)	(563,968)
Sale of fixed maturities										386,385	613,322	148,608
Net cash provided by (used in) investing activities										123,375	59,784	(1,215,360)
Cash flows from financing activities:
Net proceeds from convertible senior notes										0	0	484,625
Common stock shares issued										0	0	663,335
Repayment of long-term debt										(73,957)	(21,767)	(17,235)
Excess tax benefits related to share-based compensation										2,117	0	0
Net cash (used in) provided by financing activities										(71,840)	(21,767)	1,130,725
Net decrease in cash and cash equivalents										8,910	(10,218)	(155,155)
Cash and cash equivalents at beginning of year					$ 10,507				$ 20,725	10,507	20,725	175,880
Cash and cash equivalents at end of year		$ 19,417				$ 10,507				$ 19,417	$ 10,507	$ 20,725