Reconciliation of Beginning and Ending Balances for all Investments Measured at Fair Value Using Level 3 Inputs (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 4,407	$ 0
Realized Gains (Losses)	0	0
Unrealized Gains (Losses)		(42)
Purchase		4,660
Sales		(211)
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	(4,407)
Ending Balance		4,407
Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	4,407
Realized Gains (Losses)	0
Settlements	0
Transfers into Level 3	0
Transfers out of Level 3	(4,407)
Commercial mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Realized Gains (Losses)		0
Unrealized Gains (Losses)		(42)
Purchase		4,660
Sales		(211)
Settlements		0
Transfers into Level 3		0
Ending Balance		$ 4,407

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Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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-Publisher FASB

-Name Accounting Standards Codification

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Amount of gain (loss) recognized in other comprehensive income (loss) for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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