Condensed Consolidating Financial Information - Guarantor Subsidiaries - Condensed Consolidated Statements of Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Condensed Financial Statements, Captions [Line Items]
Net loss	$ (7,093)	$ (3,273)	$ (24,075)	$ (18,521)
Unrealized gain (loss) on short-term investments	(107)	167	363	329
Currency translation adjustments	160	0	627	0
Changes in pension plan asset and benefit obligation	7	23	(1)	22
Tax effect of the above-listed adjustments	100	(68)	(85)	(127)
Total comprehensive (loss) income	(6,933)	(3,151)	(23,171)	(18,297)
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net loss	(6,064)	(14,613)	(8,163)	(17,243)
Total comprehensive (loss) income	(6,064)	(14,613)	(8,163)	(17,243)
Parent Company Only (issuer) [Member]
Condensed Financial Statements, Captions [Line Items]
Net loss	(7,093)	(3,273)	(24,075)	(18,521)
Unrealized gain (loss) on short-term investments	(107)	167	363	329
Currency translation adjustments	0		0
Changes in pension plan asset and benefit obligation	7	23	(1)	22
Tax effect of the above-listed adjustments	100	(68)	(85)	(127)
Total comprehensive (loss) income	(7,093)	(3,151)	(23,798)	(18,297)
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net loss	7,198	15,770	7,376	17,381
Total comprehensive (loss) income	7,198	15,770	7,376	17,381
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net loss	(1,134)	(1,157)	787	(138)
Currency translation adjustments	160		627
Total comprehensive (loss) income	$ (974)	$ (1,157)	$ 1,414	$ (138)

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Amount before tax, after reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Amount of tax expense (benefit) allocated to other comprehensive income (loss).

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