Income Tax Expense - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($)
Income Tax Disclosure [Abstract]
Unrecognized tax benefits as of December 31, 2017	$ 525
Additions for tax positions of current year	61
Additions for tax positions of prior years	(2)
Reductions for settlements with taxing authorities	0
Reductions for lapses of the applicable statutes of limitations	0
Unrecognized tax benefits as of September 30, 2018	$ 584

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Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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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

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

+ References

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-Name Accounting Standards Codification
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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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