Debt (Details) (USD $)	3 Months Ended	9 Months Ended												3 Months Ended	9 Months Ended			12 Months Ended	9 Months Ended		12 Months Ended	3 Months Ended	9 Months Ended		12 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Par Value [Member]	Dec. 31, 2013 Par Value [Member]	Sep. 30, 2014 Fair Value [Member]	Dec. 31, 2013 Fair Value [Member]	Sep. 30, 2014 Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Dec. 31, 2013 Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Sep. 30, 2014 Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2013 Significant Other Observable Inputs (Level 2) [Member]	Sep. 30, 2014 Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2013 Significant Unobservable Inputs (Level 3) [Member]	Mar. 31, 2014 Senior Notes [Member]	Sep. 30, 2014 Senior Notes [Member]	Sep. 30, 2013 Senior Notes [Member]	Sep. 30, 2014 Senior Notes [Member] Senior Notes Due 2015 [Member]	Dec. 31, 2013 Senior Notes [Member] Senior Notes Due 2015 [Member]	Sep. 30, 2014 Convertible Senior Notes Due 2017 [Member]	Sep. 30, 2013 Convertible Senior Notes Due 2017 [Member]	Dec. 31, 2013 Convertible Senior Notes Due 2017 [Member]	Mar. 31, 2013 Convertible Senior Notes - Due April 2020 [Member]	Sep. 30, 2014 Convertible Senior Notes - Due April 2020 [Member]	Sep. 30, 2013 Convertible Senior Notes - Due April 2020 [Member]	Dec. 31, 2013 Convertible Senior Notes - Due April 2020 [Member]	Sep. 30, 2014 Convertible Junior Subordinated Debentures Due 2063 [Member] Period	Mar. 31, 2013 Convertible Junior Subordinated Debentures Due 2063 [Member]	Sep. 30, 2014 Convertible Junior Subordinated Debentures Due 2063 [Member] Period	Sep. 30, 2013 Convertible Junior Subordinated Debentures Due 2063 [Member]	Dec. 31, 2013 Convertible Junior Subordinated Debentures Due 2063 [Member]
Debt Instrument [Line Items]
Outstanding principal amount																	$ 62,000,000	$ 82,900,000	$ 345,000,000		$ 345,000,000	$ 500,000,000	$ 500,000,000		$ 500,000,000	$ 389,500,000		$ 389,500,000		$ 389,500,000
Repurchase of debt instrument														20,900,000
Stated interest rate (in hundredths)																	5.375%	5.375%	5.00%		5.00%	2.00%	2.00%		2.00%	9.00%		9.00%		9.00%
Maturity date																	Nov. 01, 2015	Nov. 01, 2015	May 01, 2017		May 01, 2017		Apr. 01, 2020		Apr. 01, 2020			Apr. 01, 2063		Apr. 01, 2063
Interest payments made														300,000	1,700,000	2,800,000			8,600,000	8,600,000			5,000,000	0				17,500,000	35,800,000
Conversion rate (in shares per $1,000 note)																			74.4186				143.8332					74.0741
Principal amount of notes used in determining conversion rate																			1,000				1,000			1,000		1,000
Initial conversion price (in dollars per share)																			$ 13.44				$ 6.95			$ 13.5		$ 13.5
130% of conversion price (in dollars per share)																							$ 9.03
Net proceeds from convertible senior notes		0	484,625,000																			484,600,000
Redemption price, percentage (in hundredths)																							100.00%					100.00%
Percentage of conversion price (in hundredths)																							130.00%			130.00%		130.00%
Minimum number of trading days																							20 days					20 days
Maximum number of trading days																							30 days					30 days
Minimum number of consecutive interest periods for which interest payments may be deferred																										1		1
Maximum period for which interest payments may be deferred without giving rise to an event of default																										10 years
Interest payment deferred																											18,300,000
Interest payment due on the debentures																											17,500,000
Period preceding election to convert																												5 days
Holding company cash and investments	517,000,000	517,000,000
Unrealized gain loss on holding company investments	4,500,000	4,500,000
Modified duration of holding company investments	3 years 3 months 18 days
Liabilities [Abstract]
Senior Notes				61,953,000	82,883,000	63,696,000	85,991,000	0	85,991,000	63,696,000	0	0	0
Convertible Senior Notes due 2017				345,000,000	345,000,000	374,498,000	388,988,000	374,498,000	388,988,000	0	0	0	0
Convertible Senior Notes due 2020				500,000,000	500,000,000	656,250,000	685,625,000	656,250,000	685,625,000	0	0	0	0
Convertible Junior Subordinated Debentures				389,522,000	389,522,000	497,371,000	439,186,000	0	0	497,371,000	439,186,000	0	0
Total Debt				$ 1,296,475,000	$ 1,317,405,000	$ 1,591,815,000	$ 1,599,790,000	$ 1,030,748,000	$ 1,160,604,000	$ 561,067,000	$ 439,186,000	$ 0	$ 0