STOCKHOLDERS' EQUITY AND ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Changes in Accumulated Other Comprehensive Income by component (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (148,345)
Amounts reclassified from accumulated other comprehensive income	1,742	799
Balance at end of period	(146,603)
Defined benefit plans adjustment | Pension
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(44,718)
Amounts reclassified from accumulated other comprehensive income	741
Balance at end of period	(43,977)
Defined benefit plans adjustment | Postretirement Medical Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(77,528)
Amounts reclassified from accumulated other comprehensive income	1,001
Balance at end of period	(76,527)
Available for sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	57
Amounts reclassified from accumulated other comprehensive income	0
Balance at end of period	57
Tax effect of other comprehensive income gains
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(26,156)
Amounts reclassified from accumulated other comprehensive income	0
Balance at end of period	$ (26,156)