Debt - Summary of Interest Paid (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Debt Instrument [Line Items]
Total interest payments	$ 25.6	$ 32.2
Line of Credit \| Revolving Credit Facility
Debt Instrument [Line Items]
Total interest payments	0.3	0.5
FHLB Advance
Debt Instrument [Line Items]
Total interest payments	1.5	1.5
5% Notes
Debt Instrument [Line Items]
Total interest payments	0.0	$ 3.6
Stated interest rate		5.00%
2% Notes
Debt Instrument [Line Items]
Total interest payments	0.0	$ 2.1
Stated interest rate		2.00%
Senior Notes \| 5.75% Senior Notes Due 2023
Debt Instrument [Line Items]
Total interest payments	$ 12.2	$ 12.9
Stated interest rate	5.75%
9% Debentures
Debt Instrument [Line Items]
Total interest payments	$ 11.6	$ 11.6
Stated interest rate	9.00%

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Amount of cash paid for interest. Includes, but is not limited to, payment to settle zero-coupon bond attributable to accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4297-108586

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3536-108585

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