CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
AOCI - Beginning Balance		$ (20,882)	$ (21,276)	$ (24,158)
Reclassifications		1,882	2,253	2,668
AOCI - Ending Balance		(30,964)	(20,882)	(21,276)
Accumulated Defined Benefit Pension Items
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
AOCI - Beginning Balance		(20,882)	(21,276)	(24,158)
Before Reclassifications		(7,872)	(1,859)	214
Reclassifications		1,882	2,253	2,668
Other Comprehensive Income (Loss)		(5,990)	394	2,882
Cumulative effect of change in accounting principle	[1]	(4,092)	0	0
AOCI - Ending Balance		$ (30,964)	$ (20,882)	$ (21,276)

[1] The cumulative effect of change in accounting principle relates to the adoption of ASU 2018-02, Income Statement—Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. See Note 1 - "Summary of Significant Accounting Policies" for more information.