Borrowings (Details) $ in Millions	12 Months Ended
Dec. 31, 2015 USD ($) item
Short-term Debt [Line Items]
Uncommitted secured lines of credit	$ 980.0
Number of banks \| item	7
Daily borrowings under our uncommitted secured lines	$ 496.5
Compensating balances	0.0
Trading securities pledged	1,100.0
Committed revolving credit facility	100.0
Outstanding on our revolving credit facility	$ 0.0
Maturity date	Dec. 31, 2022
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
LIBOR rate	2.00%
Company Owned Securities [Member]
Short-term Debt [Line Items]
Trading securities pledged	$ 248.5
Federal Home Loan Bank advances [Member]
Short-term Debt [Line Items]
Weighted average interest rate on borrowings	0.31%
Term Loans [Member] \| LIBOR [Member]
Short-term Debt [Line Items]
Maturity date	Jun. 03, 2016
Term Loans [Member] \| Minimum [Member] \| LIBOR [Member]
Short-term Debt [Line Items]
Interest on restated credit agreement	1.68%
Term Loans [Member] \| Maximum [Member] \| LIBOR [Member]
Short-term Debt [Line Items]
Interest on restated credit agreement	1.92%

Daily borrowings under credit arrangements.

No definition available.

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- Definition

Number of banks with which entity has committed revolving credit facility.

+ References

No definition available.

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- Definition

Uncommitted secured lines of credit.

+ References

No definition available.

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- Definition

Weighted average interest rate on borrowings.

+ References

No definition available.

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- Definition

The amount of a specific compensating balance arrangement that is maintained under an agreement for a bank loan or future credit availability.

+ References

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 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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The average effective interest rate during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
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-Subparagraph (SX 210.9-03.16)
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 20, 22
-Article 5

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

The fair value of trading securities that serve as collateral for borrowings.

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-Publisher FASB
-Name Accounting Standards Codification
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