Income Taxes - Summary of Gross Unrecognized Tax Benefits (Excluding Interest and Penalties) (Detail) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance, December 31, 2012 (excluding interest and penalties of $0.5 million)	$ 3,250,000us-gaap_UnrecognizedTaxBenefits	$ 3,250,000us-gaap_UnrecognizedTaxBenefits
Increases for prior year tax positions	0	0
Decreases for prior year tax positions	0	0
Increases for current year tax positions	0	0
Settlements	0	0
Lapse of statute of limitations	3,250,000
Balance, December 31, 2013 (excluding interest and penalties of $0.6 million)	$ 0us-gaap_UnrecognizedTaxBenefits	$ 3,250,000us-gaap_UnrecognizedTaxBenefits

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Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Unrecognized Tax Benefit

-URI http://asc.fasb.org/extlink&oid=6527854

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-Publisher FASB

-Name Accounting Standards Codification

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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-Name Accounting Standards Codification

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