SHAREHOLDERS' 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, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (63,595)
Other comprehensive income before reclassifications	(138)
Amounts reclassified from accumulated other comprehensive income (loss)	364
Balance at end of period	(63,369)
Defined benefit plans adjustment | Pension
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(12,255)
Amounts reclassified from accumulated other comprehensive income (loss)	359
Balance at end of period	(11,896)
Defined benefit plans adjustment | Postretirement Medical Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(20,292)
Amounts reclassified from accumulated other comprehensive income (loss)	5
Balance at end of period	(20,287)
Tax effect of other comprehensive income gains
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(31,048)
Other comprehensive income before reclassifications	(138)
Balance at end of period	$ (31,186)