Condensed Consolidating Financial Information - Guarantor Subsidiaries - Condensed Consolidated Statements of Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Net earnings (loss)	$ 29,330	$ (3,277)	$ (3,273)	$ (15,248)	$ (17,058)	$ (4,967)	$ 4,277	$ (8,932)	$ 7,532	$ (26,680)	$ 26,924
Unrealized gain (loss) on short-term investments									310	241	(641)
Other unrealized gain									0	0	24
Changes in pension plan assets and benefit obligations									(3)	(39)	7
Tax effect									(109)	(113)	254
Total comprehensive (loss) income									7,730	(26,591)	26,568
Parent Company Only (issuer) [Member]
Condensed Financial Statements, Captions [Line Items]
Net earnings (loss)									7,532	(26,680)	26,924
Unrealized gain (loss) on short-term investments									310	241	(641)
Other unrealized gain											24
Changes in pension plan assets and benefit obligations									(3)	(39)	7
Tax effect									(109)	(113)	254
Total comprehensive (loss) income									7,730	(26,591)	26,568
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net earnings (loss)									38,196	29,179	33,007
Total comprehensive (loss) income									38,196	29,179	33,007
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net earnings (loss)									357	(6,997)	(1,782)
Total comprehensive (loss) income									357	(6,997)	(1,782)
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net earnings (loss)									(38,553)	(22,182)	(31,225)
Total comprehensive (loss) income									$ (38,553)	$ (22,182)	$ (31,225)