Condensed Consolidating Financial Information - Guarantor Subsidiaries - Condensed Consolidating Statements of Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Condensed Financial Statements, Captions [Line Items]
Net earnings	$ 13,368		$ 19,516		$ 8,047		$ 28,354
Unrealized gain (loss) on short-term investments	25		(70)		39		(38)
Changes in pension plan assets and benefit obligations	11		(3)		9		(10)
Tax effect	(14)		29		(19)		19
Total Comprehensive Income	13,390		19,472		8,076		28,325
Parent Company Only (issuer) [Member]
Condensed Financial Statements, Captions [Line Items]
Net earnings	13,368		19,769		8,047		28,607
Unrealized gain (loss) on short-term investments	25		(70)		39		(38)
Changes in pension plan assets and benefit obligations	11		(3)		9		(10)
Tax effect	(14)		29		(19)		19
Total Comprehensive Income	13,390		19,472		8,076		28,607
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Net earnings	10,111	[1]	4,269	[1]	12,846	[1]	8,608	[1]
Unrealized gain (loss) on short-term investments		[1]		[1]		[1]		[1]
Changes in pension plan assets and benefit obligations		[1]		[1]		[1]		[1]
Tax effect		[1]		[1]		[1]		[1]
Total Comprehensive Income	10,111	[1]	4,522	[1]	12,846	[1]	8,608	[1]
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Net earnings	(10,111)		(4,522)		(12,846)		(8,861)
Unrealized gain (loss) on short-term investments
Changes in pension plan assets and benefit obligations
Tax effect
Total Comprehensive Income	$ (10,111)		$ (4,522)		$ (12,846)		$ (8,861)

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