SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated other comprehensive income (loss)
Stockholders' Equity Attributable to Parent, Beginning Balance	$ 680,299
Adjust funded status of pension plan, net of tax	5,251	$ (809)	$ (724)
Adjust funded status of pension plan, tax	700	700	600
Foreign currency translation adjustment	(687)	26	4
Unrealized Gain on Marketable Securities	868
Stockholders' Equity Attributable to Parent, Ending Balance	677,055	680,299
Short Term Investments
Accumulated other comprehensive income (loss)
Unrealized Gain on Marketable Securities	868
Stockholders' Equity Attributable to Parent, Ending Balance	868
Projected Pension Benefit Obligation
Accumulated other comprehensive income (loss)
Stockholders' Equity Attributable to Parent, Beginning Balance	(3,481)	(2,672)	(1,949)
Adjust funded status of pension plan, net of tax	5,251	(809)	(723)
Stockholders' Equity Attributable to Parent, Ending Balance	1,770	(3,481)	(2,672)
Amounts reclassified from accumulated other comprehensive income, net of tax	1,300	200	200
Translation Adjustment
Accumulated other comprehensive income (loss)
Stockholders' Equity Attributable to Parent, Beginning Balance	(223)	(249)	(253)
Foreign currency translation adjustment	(687)	26	4
Stockholders' Equity Attributable to Parent, Ending Balance	(910)	(223)	(249)
Accumulated Other Comprehensive Income/(Loss)
Accumulated other comprehensive income (loss)
Stockholders' Equity Attributable to Parent, Beginning Balance	(3,704)	(2,921)	(2,202)
Adjust funded status of pension plan, net of tax	5,251	(809)	(723)
Foreign currency translation adjustment	(687)	26	4
Unrealized Gain on Marketable Securities	868
Stockholders' Equity Attributable to Parent, Ending Balance	$ 1,728	$ (3,704)	$ (2,921)