Schedule II - Condensed Financial Information of Registrant Condensed Statements of Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net Income	$ 57,798	$ 86,248	$ 42,933
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation, Depletion and Amortization, Nonproduction	18,404	18,970	11,580
Net realized gains on investments, excluding other than temporary impairment (OTTI) losses	6,454	18,641	(23,726)
Loss on Extinguishment of Debt	0	0	(292)
Share-based Compensation	6,552	9,339	11,993
Employee Stock Ownership Plan (ESOP), Compensation Expense	1,100	1,300	800
Deferred Income Tax Expense (Benefit)	(52,336)	(80,869)	(118,048)
Increase (Decrease) in Other Operating Assets and Liabilities, Net [Abstract]
Increase (Decrease) in Other Operating Assets	(7,090)	5,005	(26,516)
Change in other liabilities	5,927	(77,082)	64,776
Net Cash Provided by (Used in) Operating Activities	784,314	277,791	420,475
Net Cash Provided by (Used in) Investing Activities [Abstract]
Payments to Acquire Property, Plant, and Equipment	(738)	(5,265)	(5,318)
Net Cash Provided by (Used in) Investing Activities	(2,129,490)	(3,605,833)	(3,116,388)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Repayments of Notes Payable	0	(46,251)	(156,641)
Purchase of 2015 notes hedges	0	0	(37,000)
Repayment of subordinated debentures	(1,141)	0	0
Excess tax benefits realized from share-based compensation plans	481	1,061	480
Proceeds from Issuance of Common Stock	5,741	4,686	6,124
Proceeds from Issuance of Warrants	0	0	15,600
Payments of Financing Costs	0	(1,566)	(6,800)
Payments of Dividends, Common Stock	9,203	6,916	5,643
Net cash provided by financing activities	2,208,769	3,135,228	2,765,677
Proceeds from Notes Payable	0	0	200,000
Cash and Cash Equivalents, Period Increase (Decrease)	863,593	(192,814)	69,764
Cash and cash equivalents at beginning of period	404,952	597,766	528,002
Cash and cash equivalents at end of period	1,268,545	404,952	597,766
Supplemental Cash Flow Information [Abstract]
Interest expense	27,666	30,650	25,802
Non cash financing activities: [Abstract]
Conversion of subordinated debentures	19,591		56
Parent Company [Member]
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net Income	57,798	86,248	42,933
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
2015 Notes Embedded Derivatives, Gain (Loss), Net	(2,488)	(21,002)	29,595
Depreciation, Depletion and Amortization, Nonproduction	2,382	2,395	1,270
Accrual of Discount on Equity Securities	(5)	(5)	(4)
Equity in Undistributed Income of Subsidiaries	(65,777)	(97,314)	(52,832)
Accretion (Amortization) of Discounts and Premiums, Investments	0	1,005	185
2015 Notes Hedges, Gain (Loss), Net	7,472	21,002	(29,595)
Net realized gains on investments, excluding other than temporary impairment (OTTI) losses	0	(18)	(13)
Loss on Extinguishment of Debt	0	0	(292)
Accrual of Discount on Debenture Issued to Subsidiary Trust	110	158	148
Amortization of Debt Discount (Premium)	12,261	13,024	7,761
Share-based Compensation	1,348	866	1,087
Employee Stock Ownership Plan (ESOP), Compensation Expense	45	45	82
Deferred Income Tax Expense (Benefit)	(2,838)	(4,355)	(5,153)
Increase (Decrease) in Other Operating Assets and Liabilities, Net [Abstract]
Increase (Decrease) in Accounts Receivable, Related Parties	1,205	1,596	(10)
Increase (Decrease) in Income Taxes Receivable	(2,745)	142	(2,296)
Increase (Decrease) in Other Operating Assets	(549)	1,702	(1,925)
Change in other liabilities	(4,469)	(1,562)	3,708
Net Cash Provided by (Used in) Operating Activities	3,750	3,927	(4,767)
Net Cash Provided by (Used in) Investing Activities [Abstract]
Capital Contributions to Subsidiaries	0	(2,450)	(2,400)
Payments to Acquire Available-for-sale Securities	0	(53,610)	(50,260)
Proceeds from Sale of Available-for-sale Securities	0	52,623	50,088
Payments to Acquire Property, Plant, and Equipment	0	0	(33)
Net Cash Provided by (Used in) Investing Activities	0	(3,437)	(2,605)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Repayments of Notes Payable	0	(46,251)	(156,641)
Purchase of 2015 notes hedges	0	0	(37,000)
Repayment of subordinated debentures	(1,141)	0	0
Excess tax benefits realized from share-based compensation plans	6	28	31
Proceeds from Issuance of Common Stock	5,370	4,686	6,123
Proceeds from Issuance of Warrants	0	0	15,600
Payments of Financing Costs	0	(1,566)	(6,800)
Payments of Dividends, Common Stock	(9,374)	(7,102)	(5,829)
Net cash provided by financing activities	(5,139)	(50,205)	15,484
Proceeds from Notes Payable	0	0	200,000
Cash and Cash Equivalents, Period Increase (Decrease)	(1,389)	(49,715)	8,112
Cash and cash equivalents at beginning of period	12,609	62,324	54,212
Cash and cash equivalents at end of period	11,220	12,609	62,324
Non cash financing activities: [Abstract]
Conversion of subordinated debentures	20,770	0	60
Convertible Notes Payable [Member] | Parent Company [Member]
Supplemental Cash Flow Information [Abstract]
Interest expense	14,564	16,917	11,085
Convertible Subordinated Debt [Member] | Parent Company [Member]
Supplemental Cash Flow Information [Abstract]
Interest expense	$ 13,102	$ 13,703	$ 14,717