Credit facility interest rate.

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Line of credit facility covenant, required underwriting reserve.

+ References

No definition available.

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Line of credit facility extended period.

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Number of tranches.

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Carrying amount as of the balance sheet date of cash collateral held for borrowed securities, for which the cash is restricted as to withdrawal or usage.

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- Definition

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

+ References

No definition available.

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- Definition

States whether the entity was in compliance with the debt covenants throughout the reporting period, and describes facts and circumstances of any compliance failure.

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Face (par) amount of debt instrument at time of issuance.

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

+ References

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- Definition

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

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Amount, after accumulated amortization, of debt discount.

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- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

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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.

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- Definition

Identification of whether the entity has been in compliance with any credit facility debt covenants during the period.

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Description of the conditions for borrowing under the credit facility including the nature of any restrictions.

+ References

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- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

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- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

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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.

+ Details

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- Definition

The cash inflow from a borrowing with the highest claim on the assets of the entity in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle, if longer).

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Debt - Additional Information (Detail) £ in Millions, $ in Millions					12 Months Ended
	Nov. 07, 2018 USD ($) Tranche	Nov. 07, 2016	Nov. 04, 2016 GBP (£)	Oct. 04, 2013 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 GBP (£)	Dec. 31, 2018 AUD ($)	Nov. 07, 2018 GBP (£) Tranche	Dec. 31, 2017 USD ($)
Line of Credit Facility [Line Items]
Issuance of new letters of credit, expiry date					Dec. 31, 2020
Line of credit facility, covenant terms					The Bilateral and Club Facilities contain customary covenants for facilities of this type, including restrictions on indebtedness and liens, limitations on mergers, dividends and the sale of assets, and requirements as to maintaining certain consolidated tangible net worth, statutory surplus and other financial ratios. These credit facilities also provide for customary events of default, including failure to pay principal, interest or fees when due, failure to comply with covenants, any representation or warranty made by our Company being false in any material respect, default under certain other indebtedness, certain insolvency or receivership events affecting our Company and our subsidiaries, the occurrence of certain material judgments, or a change in control of our Company. During the first quarter of 2018, the Company reclassified certain overseas deposits from Short-Term Investments to Other Invested Assets. Refer to Note 1 Organization & Summary of Significant Accounting Policies. Although the nature of the investments did not change, this reclassification caused the Company to exceed a covenant of our Club Facility that sets a limitation on other investments as a percentage of total investments. During the second quarter of 2018, our Company received a waiver of compliance with respect to this covenant, which was subsequently amended to increase the percentage of other investments permitted. As of December 31, 2018, our Company was in compliance with all covenants.
Senior Notes
Line of Credit Facility [Line Items]
Unamortized discount					$ 900,000				$ 1,100,000
5.75% Senior Notes
Line of Credit Facility [Line Items]
Interest rate stated on senior notes					5.75%	5.75%	5.75%
Senior notes due date					Oct. 15, 2023
5.75% Senior Notes \| Senior Notes
Line of Credit Facility [Line Items]
Principal amount of senior notes				$ 265,000,000
Interest rate stated on senior notes				5.75%
Net proceeds from issuance of senior notes				$ 263,300,000
Debt instrument, covenant compliance					As of December 31, 2018, our Company was in compliance with all such covenants
7.0% Senior Notes \| Senior Notes
Line of Credit Facility [Line Items]
Interest rate stated on senior notes					7.00%	7.00%	7.00%
Senior notes due date					May 01, 2016
Call premium on redemption of Senior notes					$ 17,900,000
Club Facility
Line of Credit Facility [Line Items]
Number of tranches \| Tranche	2							2
Club Facility \| Minimum
Line of Credit Facility [Line Items]
Credit facility fee rate	0.95%
Club Facility \| Maximum
Line of Credit Facility [Line Items]
Credit facility fee rate	1.60%
Club Facility \| Tranche One Extending
Line of Credit Facility [Line Items]
Line of credit, commitment	$ 165,000,000
Club Facility \| Tranche Two Extending
Line of Credit Facility [Line Items]
Line of credit, commitment \| £								£ 60.0
Bilateral Facility
Line of Credit Facility [Line Items]
Line of credit facility	$ 25,000,000
Additional extended term		2 years
Bilateral Facility \| Minimum
Line of Credit Facility [Line Items]
Credit facility fee rate	0.85%
Bilateral Facility \| Maximum
Line of Credit Facility [Line Items]
Credit facility fee rate	1.20%
Syndicate 1221
Line of Credit Facility [Line Items]
Aggregate face amount of letters of credit outstanding							$ 24.0
Line of credit facility, covenant compliance					As of December 31, 2018, our Company was in compliance with all covenants.
Syndicate 1221 \| Line of Credit
Line of Credit Facility [Line Items]
Line of credit facility, interest rate			1.55%
Lloyd's \| Syndicate 1221
Line of Credit Facility [Line Items]
Line of credit facility, underwriting reserve required \| £			£ 75.0
Lloyd's \| Syndicate 1221 \| Club Facility
Line of Credit Facility [Line Items]
Aggregate face amount of letters of credit outstanding					$ 165,000,000	£ 60.0
Cash collateral posted					1,200,000
Lloyd's \| Syndicate 1221 \| Bilateral Facility
Line of Credit Facility [Line Items]
Aggregate face amount of letters of credit outstanding					$ 8,000,000