Commitments and Contingencies - Future Minimum Rental Receipts Under Non - Cancelable Lease Agreements (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Future minimum rental receipts under non-cancelable lease agreements
2016	$ 835
2017	848
2018	862
2019	492
2020	305
Thereafter	0
Total	$ 3,342

Future minimum rental payments in aggregate as of the balance sheet date under operating leases.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6454179&loc=d3e41551-112718

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

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- Definition

Future rental payments receivable within one year of the balance sheet date under an operating lease.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Future rental payments receivable within the fifth year from the balance sheet date under an operating lease.

+ References

+ Details

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Namespace Prefix:	us-gaap_
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- Definition

Future rental payments receivable within the fourth year from the balance sheet date under an operating lease.

+ References

+ Details

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- Definition

Future rental payments receivable within the third year from the balance sheet date under an operating lease.

+ References

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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- Definition

Future rental payments receivable within the second year from the balance sheet date under an operating lease.

+ References

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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- Definition

Future minimum lease payments receivable under operating leases for periods greater than five years following the balance sheet date.

+ References

+ Details

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Namespace Prefix:	us-gaap_
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