Condensed Consolidating Financial Information - Guarantor Subsidiaries - Condensed Consolidating Statements of Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Net earnings	$ 7,392	$ 17,249	$ 13,368	$ (5,321)	$ 16,825	$ 13,777	$ 19,516	$ 8,838	$ 32,688		$ 58,956		$ 18,057
Unrealized gain on short-term investments									(285)		44		92
Other unrealized loss									24
Changes in pension plan assets and benefit obligations									17		(2)		(22)
Tax impact									105		(15)		(28)
Total comprehensive income									32,501		58,983		18,099
Parent Company Only (issuer) [Member]
Condensed Financial Statements, Captions [Line Items]
Net earnings									32,688		58,956		18,057
Unrealized gain on short-term investments									(285)		44		92
Other unrealized loss									24
Changes in pension plan assets and benefit obligations									17		(2)		(22)
Tax impact									105		(15)		(28)
Total comprehensive income									32,501		58,983		18,099
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net earnings									38,740	[1]	15,567	[1]	15,714	[1]
Total comprehensive income									38,740	[1]	15,567	[1]	15,714	[1]
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net earnings									(38,740)		(15,567)		(15,714)
Total comprehensive income									$ (38,740)		$ (15,567)		$ (15,714)

[1] Foreign subsidiaries represent minor subsidiaries and are included in the guarantors' subsidiaries amounts.