Revenue Recognition - Additional Information (Detail) - Topic 606 [Member] - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2017
Summary Of Accounting Policies [Line Items]
Cumulative-effect adjustment to retained earnings					$ 404,000
Asset impairment charges related to contract assets	$ 0	$ 0	$ 0	$ 0
Amortization of contract acquisition costs	7,000	12,000	93,000	160,000
Asset impairment charges for contract acquisition cost	$ 0	$ 0	$ 0	$ 0
Revenue practical expedient, incremental cost of obtaining contract [true/false]			true
Revenue, remaining performance obligation, optional exemption, performance obligation [true/false]			true

Summary of accounting policies.

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Amount of amortization expense for asset recognized from cost incurred to obtain or fulfill contract with customer.

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Amount of impairment loss for asset recognized from cost incurred to obtain or fulfill contract with customer.

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Amount of cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

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- Definition

Indicates (true false) whether practical expedient was elected to recognize incremental cost of obtaining contract as expense when incurred if amortization period would have been one year or less.

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Indicates (true false) whether optional exemption was applied not to disclose amount of transaction price allocated to and explanation of expected timing of revenue recognition for remaining performance obligation, when contract has expected duration of one year or less or right to consideration corresponds directly to performance completed.

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