Reinsurance Ceded (Details 2) (USD $) In Millions, unless otherwise specified	Jun. 30, 2011	Dec. 31, 2010
Reinsurance Ceded
Reinsurance recoverable overdue by more than 90 days	$ 14.1
Reinsurance recoverable overdue by more than 90 days, collateralized amount	6.4
Amount of reinsurance recoverable secured by funds held, trust agreements and letters of credit	410.4
Reinsurance recoverable that is overdue, minimum number of days overdue (in days)	90
Allowance for estimated unrecoverable reinsurance
Reinsurance Ceded
Allowance for estimated unrecoverable reinsurance on paid and unpaid losses	$ 12.0	$ 12.0
Reinsurers rated "A-" or better
Reinsurance Ceded
Percentage of reinsurance recoverable on paid and unpaid losses and LAE balances due from reinsurers (as a percent)	96.00%
Reinsurers rated between "BBB+' and "B"
Reinsurance Ceded
Percentage of reinsurance recoverable on paid and unpaid losses and LAE balances due from reinsurers (as a percent)	1.00%
Reinsurers which were not rated
Reinsurance Ceded
Percentage of reinsurance recoverable on paid and unpaid losses and LAE balances due from reinsurers (as a percent)	3.00%

Represents the amount of total reinsurance recoverable secured by the collateral provided by reinsurers.

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- Definition

Represents the percentage of reinsurance recoverable, by grading of reinsurers.

+ Details

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- Details

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- Definition

Related to the reinsurance recoverable that was overdue by more than this number of days.

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents reinsurance recoverables which are overdue by more than 90 days.

+ Details

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Namespace Prefix:	trh
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the collateralized amount of reinsurance recoverables which are overdue by more than 90 days.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 09
-Article 12

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e24092-122690

+ Details

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Balance Type:	credit
Period Type:	instant