Condensed Consolidating Financial Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Condensed Consolidating Statements of Comprehensive Income [Abstract]
Net earnings	$ 8,838	$ 2,178
Unrealized gain on short-term investments	19	50
Changes in pension plan assets and benefit obligations	(4)	(4)
Total comprehensive income net of income taxes	8,853	2,224
Parent Company Only [Member]
Condensed Consolidating Statements of Comprehensive Income [Abstract]
Net earnings	8,838	2,178
Unrealized gain on short-term investments	19	50
Changes in pension plan assets and benefit obligations	(4)	(4)
Total comprehensive income net of income taxes	8,853	2,224
Guarantor Subsidiaries [Member]
Condensed Consolidating Statements of Comprehensive Income [Abstract]
Net earnings	2,744	1,756
Total comprehensive income net of income taxes	2,744	1,756
Eliminations [Member]
Condensed Consolidating Statements of Comprehensive Income [Abstract]
Net earnings	(2,744)	(1,756)
Total comprehensive income net of income taxes	$ (2,744)	$ (1,756)