Fair Value Measurements - Financial instruments not carried at fair value (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments - structured transactions	$ 354,400,000	$ 354,400,000
Deposit liabilities	1,211,203,000us-gaap_DepositContractsLiabilities	1,245,367,000us-gaap_DepositContractsLiabilities
Notes payable and debt	2,643,561,000us-gaap_LongTermDebt	1,662,580,000us-gaap_LongTermDebt
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	354,352,000	354,382,000
Deposit liabilities	1,211,203,000	1,245,367,000
Notes payable and debt	2,643,561,000	1,662,580,000
Financial Liabilities	3,854,764,000	2,907,947,000
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial Assets	367,491,000	371,625,000
Deposit liabilities	1,528,570,000	1,543,761,000
Notes payable and debt	2,957,605,000	1,897,854,000
Financial Liabilities	$ 4,486,175,000	$ 3,441,615,000

Carrying amount of liabilities as of the balance sheet date pertaining to amounts received by the insurer or reinsurer from the insured (including a ceding company) under insurance or reinsurance contracts for which insurance risk is not transferred.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 340

-SubTopic 30

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6387650&loc=d3e9420-108338

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- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 7

Reference 2: 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)

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

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 9

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 20, 22

-Article 5

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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- Definition

Aggregate value of financial instrument assets that are not carried at fair value in the financial statements.

+ References

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Aggregate value of financial instrument liabilities that are not carried at fair value in the financial statements.

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- Definition

The Other investments balance disclosed within the Fair Value Measurements tables exclude certain structured transactions including certain investments in project finance transactions, a payment obligation and liquidity financing provided to a structured credit vehicle as a part of a third party medium term note facility.

+ References

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