CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net earnings	$ 19,516	$ 6,054	$ 28,354	$ 8,232
Unrealized (loss) gain on short-term investments	(42)	17	(23)	67
Changes in pension plan assets and benefit obligations	(2)	(8)	(6)	(12)
Total comprehensive income	$ 19,472	$ 6,063	$ 28,325	$ 8,287