CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement Of Income And Comprehensive Income [Abstract]
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