SHAREHOLDERS' EQUITY AND ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Changes in Accumulated Other Comprehensive Income by component (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (63,595)
Other comprehensive income before reclassifications	9,253
Amounts reclassified from accumulated other comprehensive income (loss)	727
Balance at end of period	(53,615)
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)	717
Balance at end of period	(11,538)
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)	10
Balance at end of period	(20,282)
Foreign currency translation adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	0
Other comprehensive income before reclassifications	9,477
Balance at end of period	9,477
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	(224)
Balance at end of period	$ (31,272)