SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Short-term investments		$ 0	$ 0
Allowance for doubtful accounts receivable		600,000	600,000
Excess tax benefit from share-based compensation		400,000	300,000	$ 1,100,000
Tax Cuts And Jobs Act Of 2017, deferred tax assets, tax credit carryforward, alternative minimum tax, noncurrent receivable, net		70,700,000
Tax Cuts And Jobs Act Of 2017, deferred tax assets, tax credit carryforward, alternative minimum tax, noncurrent receivable, estimate for sequestration rate reduction		5,000,000
Inventory valuation allowance		900,000	700,000
Total assets held-for-sale		0	$ 0
Curtailment gain	$ 14,500,000	$ 14,500,000
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Yield curve, term		0 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Yield curve, term		30 years