SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($) $ in Thousands	Jan. 01, 2019	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings		$ (1,604,178)		$ (1,560,444)
Cumulative effect adjustments				(92,525)
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings			$ 92,500
Retained Earnings
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect adjustments				(81,973)
Retained Earnings | Accounting Standards Update 2016-01
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect adjustments			10,600
Accumulated Other Comprehensive Income (Loss)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect adjustments				$ (10,552)
Accumulated Other Comprehensive Income (Loss) | Accounting Standards Update 2016-01
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect adjustments			$ (10,600)
Accounting Standards Update 2016-02
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Right-of-use asset and lease liability		$ 21,000
Forecast | Retained Earnings | Accounting Standards Update 2017-08
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect adjustments	$ (56,100)