Debt (Details)		1 Months Ended	3 Months Ended
		Feb. 29, 2016 USD ($)	Mar. 31, 2016 USD ($) trading_day $ / shares shares	Mar. 31, 2015 USD ($) shares	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Antidilutive securities (in shares) | shares			23,300,000	0
Loss on debt extinguishment			$ 13,440,000	$ 0
Federal Home Loan Bank advances		$ 155,000,000
Federal Home Loan Bank, advances, interest rate		1.91%
Federal Home Loan Bank advances, collateral, value of principal, percent		102.00%
Convertible senior notes			685,624,000		$ 822,301,000
Convertible junior subordinated debentures			256,872,000		389,522,000
Total debt			1,097,500,000		1,211,800,000
Holding company cash and investments			265,000,000
Unrealized gain loss on holding company investments			$ 100,000
Modified duration of holding company investments			2 years 4 months 24 days
Interest payments made			$ 6,300,000	0
Scenario, Previously Reported
Debt Instrument [Line Items]
Total debt					1,223,000,000
Restatement Adjustment
Debt Instrument [Line Items]
Total debt					(11,200,000)
Adjustments for New Accounting Pronouncement | Long-term Debt
Debt Instrument [Line Items]
Deferred issuance costs reclassified					(11,200,000)
Adjustments for New Accounting Pronouncement | Other Assets
Debt Instrument [Line Items]
Deferred issuance costs reclassified					11,200,000
Convertible Senior Notes, interest at 5% per annum, due May 2017
Debt Instrument [Line Items]
Extinguishment of debt amount			138,300,000
Purchase price of debt purchased			$ 143,400,000
Antidilutive securities (in shares) | shares			10,300,000
Convertible senior notes					331,500,000
Total debt	[1]		$ 194,300,000		331,500,000
Conversion rate (in shares per $1,000 note) | shares			74.4186
Principal amount of notes used in determining conversion rate			$ 1,000
Initial conversion price (in dollars per share) | $ / shares			$ 13.44
Stated interest rate (in hundredths)			5.00%
Interest payments made			$ 1,800,000	0
Convertible Senior Notes, interest at 5% per annum, due May 2017 | Scenario, Previously Reported
Debt Instrument [Line Items]
Convertible senior notes					333,500,000
Convertible Senior Notes, interest at 5% per annum, due May 2017 | Restatement Adjustment
Debt Instrument [Line Items]
Convertible senior notes					(2,000,000)
Convertible Junior Debentures at 9% per annum, Due 2063
Debt Instrument [Line Items]
Extinguishment of debt amount		$ 132,700,000
Purchase price of debt purchased		$ 150,700,000
Antidilutive securities (in shares) | shares			9,800,000
Loss on debt extinguishment			$ 8,300,000
Reacquisition of convertible junior subordinated debentures-equity component			$ 9,800,000
Convertible junior subordinated debentures					389,500,000
Stated interest rate (in hundredths)			9.00%
Convertible Junior Debentures at 9% per annum, Due 2063 | Scenario, Previously Reported
Debt Instrument [Line Items]
Convertible junior subordinated debentures					389,500,000
Convertible Junior Debentures at 9% per annum, Due 2063 | Restatement Adjustment
Debt Instrument [Line Items]
Convertible junior subordinated debentures					0
FHLB Advance, interest at 1.91% per annum, due February 2023
Debt Instrument [Line Items]
Total debt			$ 155,000,000		0
Interest payments made			200,000	0
Convertible Senior Notes, interest at 2% per annum, due April 2020
Debt Instrument [Line Items]
Convertible senior notes					490,800,000
Total debt	[2],[3]		$ 491,300,000		490,800,000
Conversion rate (in shares per $1,000 note) | shares			143.8332
Principal amount of notes used in determining conversion rate			$ 1,000
Initial conversion price (in dollars per share) | $ / shares			$ 6.95
Stated interest rate (in hundredths)			2.00%
Threshold number of trading days | trading_day			20
Threshold consecutive trading days			30 days
Percentage of conversion price (in hundredths)			130.00%
Convertible debt, conversion price | $ / shares			$ 9.03
Redemption price, percentage (in hundredths)			100.00%
Interest payments made			$ 0	0
Convertible Senior Notes, interest at 2% per annum, due April 2020 | Scenario, Previously Reported
Debt Instrument [Line Items]
Convertible senior notes					500,000,000
Convertible Senior Notes, interest at 2% per annum, due April 2020 | Restatement Adjustment
Debt Instrument [Line Items]
Convertible senior notes					(9,200,000)
Convertible Junior Subordinated Debentures, interest at 9% per annum, due April 2063
Debt Instrument [Line Items]
Total debt	[4]		$ 256,900,000		$ 389,500,000
Conversion rate (in shares per $1,000 note) | shares			74.0741
Principal amount of notes used in determining conversion rate			$ 1,000
Initial conversion price (in dollars per share) | $ / shares			$ 13.50
Stated interest rate (in hundredths)			9.00%
Period preceding election to convert			5 days
Interest payments made			$ 4,300,000	$ 0

[1] Convertible at any time prior to maturity at the holder’s option, at an initial conversion rate, which is subject to adjustment, of 74.4186 shares per $1,000 principal amount, representing an initial conversion price of approximately $13.44 per share.

[2] Prior to April 10, 2017, the notes will not be redeemable. On any business day on or after April 10, 2017 we may redeem for cash all or part of the notes, at our option, at a redemption rate equal to 100% of the principal amount of the notes being redeemed, plus any accrued and unpaid interest, if the closing sale price of our common stock exceeds 130% of the then prevailing conversion price of the notes for each of at least 20 of the 30 consecutive trading days preceding notice of the redemption.

[3] Prior to January 1, 2020, the 2% Convertible Senior Notes are convertible only upon satisfaction of one or more conditions. One such condition is that during any calendar quarter commencing after March 31, 2014, the last reported sale price of our common stock for each of at least 20 trading days during the 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter be greater than or equal to 130% of the applicable conversion price on each applicable trading day. The 2% Notes are convertible at an initial conversion rate, which is subject to adjustment, of 143.8332 shares per $1,000 principal amount, representing an initial conversion price of approximately $6.95 per share. 130% of such conversion price is $9.03. On or after January 1, 2020, holders may convert their notes irrespective of satisfaction of the conditions.

[4] Convertible at any time prior to maturity at the holder’s option, at an initial conversion rate, which is subject to adjustment, of 74.0741 shares per $1,000 principal amount, representing an initial conversion price of approximately $13.50 per share. If a holder elects to convert their debentures, deferred interest owed on the debentures being converted is also converted into shares of our common stock. The conversion rate for any deferred interest is based on the average price that our shares traded at during a 5-day period immediately prior to the election to convert. In lieu of issuing shares of common stock upon conversion of the debentures, we may, at our option, make a cash payment to converting holders for all or some of the shares of our common stock otherwise issuable upon conversion.