FINANCIAL ASSETS AND LIABILITIES - Fair Values (Details) - USD ($) $ in Thousands | Jun. 30, 2017 | Dec. 31, 2016 |
Estimate of Fair Value Measurement [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash and Cash Equivalents, Fair Value Disclosure | $ 122,699 | $ 212,942 |
Restricted cash and investments, Fair Value Disclosure | 68,529 | 54,112 |
Reported Value Measurement [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash and Cash Equivalents, Fair Value Disclosure | 122,699 | 212,942 |
Restricted cash and investments, Fair Value Disclosure | 68,529 | 54,112 |
Secured Debt [Member] | Estimate of Fair Value Measurement [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 1,087,371 | 886,468 |
Secured Debt [Member] | Reported Value Measurement [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 1,087,371 | 886,468 |
Convertible Debt | Estimate of Fair Value Measurement [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 179,914 | 162,122 |
Convertible Debt | Reported Value Measurement [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 182,286 | 177,300 |
Seller's Credit [Member] | Estimate of Fair Value Measurement [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 22,500 | 0 |
Seller's Credit [Member] | Reported Value Measurement [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 22,500 | 0 |
Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash and Cash Equivalents, Fair Value Disclosure | 122,699 | 212,942 |
Restricted cash and investments, Fair Value Disclosure | 68,529 | 54,112 |
Fair Value, Measurements, Recurring [Member] | Secured Debt [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 1,087,371 | 886,468 |
Fair Value, Measurements, Recurring [Member] | Convertible Debt | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 179,914 | 162,122 |
Fair Value, Measurements, Recurring [Member] | Seller's Credit [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 22,500 | |
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash and Cash Equivalents, Fair Value Disclosure | 122,699 | 212,942 |
Restricted cash and investments, Fair Value Disclosure | 68,529 | 54,112 |
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Secured Debt [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 0 | 0 |
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Convertible Debt | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 0 | 0 |
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Seller's Credit [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 0 | |
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash and Cash Equivalents, Fair Value Disclosure | 0 | 0 |
Restricted cash and investments, Fair Value Disclosure | 0 | 0 |
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Secured Debt [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 1,087,371 | 886,468 |
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Convertible Debt | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 179,914 | 162,122 |
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Seller's Credit [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 22,500 | |
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash and Cash Equivalents, Fair Value Disclosure | 0 | 0 |
Restricted cash and investments, Fair Value Disclosure | 0 | 0 |
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Secured Debt [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 0 | 0 |
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Convertible Debt | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | 0 | $ 0 |
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Seller's Credit [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Long-term Debt, Fair Value | $ 0 | |