Ceded Reinsurance - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Effects of Reinsurance [Line Items]
Policyholders' surplus for reinsurance	$ 500,000
Reinsurance rating description	A reinsurer generally must have a rating from A.M. Best and/or S&P of “A” or better, or an equivalent financial strength if not rated, plus at least $500 million in policyholders’ surplus to meet our standards of acceptability.
Reserve for uncollectible reinsurance amount	$ 12,100	$ 6,900
Collateral Held	151,708
Ceded Balances Payable
Effects of Reinsurance [Line Items]
Collateral Held	109,000
Letter of Credit
Effects of Reinsurance [Line Items]
Collateral Held	39,700
All Others
Effects of Reinsurance [Line Items]
Collateral Held	$ 3,000

Reinsurers rating.

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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

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Amount of funds held as security for payments to be received under reinsurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.13(c))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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- Definition

Amount of policyholders' surplus excluded from calculating deferred taxes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(c)
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- Definition

Amount of valuation allowance for reinsurance recoverables. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

+ References

No definition available.

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