Fair Value Measurements (Quantitative Information Used as Level 3 Inputs) (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
Jun. 30, 2018	Dec. 31, 2017
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Total other assets and (liabilities)	$ 2,488	$ 2,542
Internal valuation model \| Fair Value (Level 3)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Total other assets and (liabilities)	2,018
Assumed and ceded (re)insurance contracts, group one \| Internal valuation model \| Fair Value (Level 3)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Other assets	$ 935
Assumed and ceded (re)insurance contracts, group one \| Internal valuation model \| Fair Value (Level 3) \| Low
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Bond price (in dollars per share)	$ 101.38
Assumed and ceded (re)insurance contracts, group one \| Internal valuation model \| Fair Value (Level 3) \| High
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Bond price (in dollars per share)	110.93
Assumed and ceded (re)insurance contracts, group one \| Internal valuation model \| Fair Value (Level 3) \| Weighted Average or Actual
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Bond price (in dollars per share)	$ 106.64
Liquidity discount	1.30%
Assumed and ceded (re)insurance contracts, group two \| Internal valuation model \| Fair Value (Level 3)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Other (liabilities)	$ (2,953)
Assumed and ceded (re)insurance contracts, group two \| Internal valuation model \| Fair Value (Level 3) \| Low
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Contract period	2 years
Assumed and ceded (re)insurance contracts, group two \| Internal valuation model \| Fair Value (Level 3) \| High
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Contract period	4 years 8 months 12 days
Assumed and ceded (re)insurance contracts, group two \| Internal valuation model \| Fair Value (Level 3) \| Weighted Average or Actual
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Net undiscounted cash flows	$ 4,815
Expected loss ratio	18.70%
Net acquisition expense ratio	13.80%
Contract period	4 years 1 month 6 days
Discount rate	2.70%

Fair Value Inputs, Expected Loss Ratio

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- Definition

Fair Value Inputs, Net Acquisition Expense Ratio

+ References

No definition available.

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- Definition

Fair Value Inputs, Net Undiscounted Cash Flows

+ References

No definition available.

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- Definition

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a recurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ References

No definition available.

+ Details

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- Definition

Period the instrument, asset or liability is expected to be outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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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.

+ References

No definition available.

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- Definition

Adjustment to the discount rate used to measure fair value for lack of ability to convert business interests into cash quickly.

+ References

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

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- Definition

Price at which a dealer is willing to buy an instrument, used as an input to measure fair value.

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- Definition

Aggregation of the liabilities reported on the balance sheet measured at fair value on a recurring basis by the entity.

+ References

No definition available.

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- Definition

Fair value portion of other assets.

+ References

No definition available.

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