SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 58,000	$ 7,272,000
Amortization of debt issuance costs	5,167,000	6,005,000	$ 5,154,000
Allowance for doubtful accounts receivable	682,000	70,000
Ineffective portion	0	0	0
OBS ABL Facility [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash		5,576,000
Debt Instrument, unamortized discount	418,000	800,000
OBS Term Loan
Summary Of Significant Accounting Policies [Line Items]
Debt Instrument, unamortized discount	$ 7,037,000	10,421,000
Vessel/Fleet [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	25 years
Interest costs capitalized	$ 0	0	$ 0
New ATBs [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	30 years
Other Property [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	3 years
Other Property [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	15 years
Drydock [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortization period for deferred costs	2 years 6 months
Drydock [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortization period for deferred costs	5 years
Bareboat Charters-In [Member]
Summary Of Significant Accounting Policies [Line Items]
Operating leases, future minimum payments due	$ 253,576,000
Unsecured Senior Notes [Member] | Notes8125 Percent Due2018 [Member]
Summary Of Significant Accounting Policies [Line Items]
Debt Instrument, unamortized discount	0	$ 1,414,000
Unsecured Senior Notes [Member] | Seven Point Five Percentage Election Two Notes Due Two Thousand Twenty One [Member]
Summary Of Significant Accounting Policies [Line Items]
Debt Instrument, unamortized discount	$ 6,000