Consolidated Statements of Comprehensive Income (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
Statement of Comprehensive Income [Abstract]
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 (loss) 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