Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended				24 Months Ended
	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, 2007	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net deferred tax assets and liabilities [Abstract]
Total deferred tax assets														$ 791,286	$ 933,576
Total deferred tax liabilities														(29,206)	(33,789)
Valuation allowance														0	(902,289)	$ (1,004,200)
Net deferred tax asset (liability)														762,080
Net deferred tax asset (liability)															(2,502)
Components of net deferred tax liability [Abstract]
Unearned premium reserves														33,262	12,296
Benefit plans														(14,283)	(13,900)
Federal net operating loss														680,975	845,616
Loss reserves														15,536	23,069
Unrealized (appreciation) depreciation in investments														(8,904)	2,800
Mortgage investments														17,386	15,346
Deferred compensation														12,927	11,955
Premium deficiency reserves														0	8,313
Other, net														(7,373)	108
Net deferred tax asset before valuation allowance														762,080	899,787
Valuation allowance														0	(902,289)	(1,004,200)
Net deferred tax asset (liability)														762,080
Change in cumulative income position														687,300
Net operating loss carryforwards, regular tax basis														1,946,000
Operating loss carryforward utilized									$ 471,000	$ 199,000
Change in deferred tax valuation allowance, included in other comprehensive income									(54,500)	(13,100)	$ 17,300
Net operating loss carryforwards for computing the alternative minimum tax														1,051,000
Tax provision (benefit) [Abstract]
Provision for (benefit from) income taxes before valuation allowance									163,497	91,607	(17,239)
Change in valuation allowance									(161,158)	(88,833)	20,935
Reversal of the valuation allowance									(686,652)	0	0
(Benefit from) provision for income taxes	$ 6,584	$ (695,604)	$ 1,322	$ 3,385	$ 681	$ 249	$ 1,118	$ 726	(684,313)	2,774	3,696
Components of provisions for (benefit from) income taxes [Abstract]
Current Federal									8,067	2,391	916
Deferred Federal									(686,652)	1	7
Other									(5,728)	382	2,773
(Benefit from) provision for income taxes	6,584	$ (695,604)	$ 1,322	3,385	681	$ 249	$ 1,118	726	(684,313)	2,774	3,696
Income taxes paid									$ 5,400	$ 1,300	$ 100
Reconciliation of effective income tax rate [Abstract]
Federal statutory income tax rate (in hundredths)									35.00%	35.00%	(35.00%)
Valuation allowance (in hundredths)									(173.80%)	(34.90%)	45.40%
Tax exempt municipal bond interest (in hundredths)									(0.80%)	(0.40%)	(3.70%)
Other, net (in hundredths)									(0.70%)	1.40%	1.30%
Effective income tax rate (in hundredths)									(140.30%)	1.10%	8.00%
Information regarding income tax examinations [Abstract]
Amount of IRS assessment for unpaid taxes and penalties related to REMIC issue														197,500
Estimate of federal interest that may be due														182,900
Amount of payment made related to the IRS assessment on the REMIC issue												$ 65,200
Amount of IRS assessment for unpaid taxes and penalties related to disallowance of carryback of 2009 net operating loss														261,400
Estimate of additional state income taxes and interest that may be due														48,800
Unrecognized tax benefits	107,120			106,230	106,230			105,366	$ 106,230	$ 105,366	$ 104,550		$ 105,366	107,120	106,230	105,366
Unrecognized tax benefits [Roll Forward]
Balance at beginning of year				$ 106,230				$ 105,366	106,230	105,366	104,550		105,366
Additions based on tax positions related to the current year									0	0	0
Additions for tax positions of prior years									890	864	816
Reductions for tax positions of prior years									0	0	0
Settlements									0	0	0
Balance at end of year	$ 107,120				$ 106,230				107,120	$ 106,230	$ 105,366		107,120
Unrecognized tax benefits [Abstract]
Total amount of unrecognized tax benefits that would affect effective tax rate														93,900
Interest expense recognized during period									$ 900
Unrecognized tax benefits, accrued interest														27,800	$ 26,900
Significant change in unrecognized tax benefits														107,100
Approximate net cash outflows upon resolution of IRS matters														26,000
Internal Revenue Service (IRS)
Components of net deferred tax liability [Abstract]
Net operating loss carryforwards, regular tax basis														$ 1,900,000		$ 2,600,000
Operating loss carryforward utilized													$ 670,000
Operating loss carryforward, recognition period									6 years
Deferred Tax Asset, Changes In Current Period
Tax provision (benefit) [Abstract]
Change in valuation allowance									$ 154,800
Deferred Tax Asset, Changes In Current Period | Other Comprehensive Income (Loss)
Tax provision (benefit) [Abstract]
Change in valuation allowance									(6,300)
Deferred Tax Asset, Changes In Current Period | Income Tax Expense (Benefit)
Tax provision (benefit) [Abstract]
Change in valuation allowance									161,100
Deferred Tax Asset, Changes In Future Periods
Tax provision (benefit) [Abstract]
Change in valuation allowance									747,500
Deferred Tax Asset, Changes In Future Periods | Other Comprehensive Income (Loss)
Tax provision (benefit) [Abstract]
Change in valuation allowance									60,800
Deferred Tax Asset, Changes In Future Periods | Income Tax Expense (Benefit)
Tax provision (benefit) [Abstract]
Change in valuation allowance									$ 686,700