Condensed Consolidating Financial Information - Guarantor Subsidiaries - Condensed Consolidated Statements of Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed Financial Statements, Captions [Line Items]
Net loss	$ (11,531)	$ (3,277)	$ (35,607)	$ (21,798)
Unrealized gain (loss) on short-term investments	0	41	363	370
Currency translation adjustments	(4,718)	0	(4,091)	0
Changes in pension plan asset and benefit obligation	0	(24)	(1)	(2)
Tax effect of the above-listed adjustments	0	(8)	(85)	(134)
Total comprehensive (loss) income	(16,249)	(3,268)	(39,421)	(21,564)
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net loss	(10,381)	(14,850)	(18,542)	(32,093)
Total comprehensive (loss) income	(10,381)	(14,850)	(18,542)	(32,093)
Parent Company Only (issuer) [Member]
Condensed Financial Statements, Captions [Line Items]
Net loss	(11,531)	(3,277)	(35,607)	(21,798)
Unrealized gain (loss) on short-term investments	0	41	363	370
Currency translation adjustments	0		0
Changes in pension plan asset and benefit obligation	0	(24)	(1)	(2)
Tax effect of the above-listed adjustments	0	(8)	(85)	(134)
Total comprehensive (loss) income	(11,531)	(3,268)	(35,330)	(21,564)
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net loss	6,684	16,305	14,059	33,686
Total comprehensive (loss) income	6,684	16,305	14,059	33,686
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net loss	3,697	(1,455)	4,483	(1,593)
Currency translation adjustments	(4,718)		(4,091)
Total comprehensive (loss) income	$ (1,021)	$ (1,455)	$ 392	$ (1,593)