FINANCIAL INSTRUMENTS - Fair value of Debt Instruments (Details) - Summit Holdings - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Carrying value | 5.5% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 297,253	$ 297,090
Carrying value | Senior Notes 5.75%
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	493,349	493,102
Fair Value | 5.5% Senior Notes | Estimated fair value (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	292,250	301,750
Fair Value | Senior Notes 5.75% | Estimated fair value (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 475,000	$ 501,667