Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
NET EARNINGS	$ 40,874	$ 23,192	$ 39,834
OTHER COMPREHENSIVE INCOME (LOSS):
Actuarial gain (loss) for retiree liabilities	(27,350)	(91,523)	2,974
Unrealized gain (loss) for derivative instruments	0	631	(848)
Reclassifications to net income	(57)	3,709	(106)
Income tax (expense) or benefit	20	(1,595)	346
TOTAL COMPREHENSIVE INCOME (LOSS)	26,634	(33,621)	39,989
Pension Plans [Member]
OTHER COMPREHENSIVE INCOME (LOSS):
Actuarial gain (loss) for retiree liabilities	(27,518)	(91,715)	(19,685)
Reclassifications to net income	10,681	2,700	2,068
Income tax (expense) or benefit	5,861	32,714	6,395
Post-Retirement Plans [Member]
OTHER COMPREHENSIVE INCOME (LOSS):
Actuarial gain (loss) for retiree liabilities	168	192	22,659
Reclassifications to net income	(5,119)	(5,341)	(3,847)
Income tax (expense) or benefit	$ 1,724	$ 1,892	$ (6,827)