Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Income Taxes [Line Items]
U.S. federal corporate statutory tax rate	21.00%		35.00%
Liability for uncertain tax positions totaled	$ 900		$ 900
Deferred income tax expense	(744)	$ (46)
Foreign Subsidiaries [Member]
Income Taxes [Line Items]
Deferred income tax expense	$ 600		$ 0

Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations.

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