Business and Segment Reporting (Reportable Segments Information) (Details) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments \| segment			2
Revenues, services	$ 71,278	$ 60,926	$ 242,162	$ 169,813
Depreciation and amortization	18,961	19,317	56,708	53,745
Loss/(gain) on disposal of vessels and other property	(1,472)	17,360	28	17,193
Adjusted income/(loss) from vessel operations	2,116	(13,236)	29,383	(36,383)
Equity in income of affiliated companies	8,474	5,338	24,559	22,500
Investments in and advances to affiliated companies	271,655	275,420	271,655	275,420
Adjusted total assets	1,699,817	1,757,701	1,699,817	1,757,701
Expenditures for vessels and vessel improvements			9,797	135,215
Payments for drydockings			13,539	3,968
Time Charter Equivalent Services [Member]
Segment Reporting Information [Line Items]
Revenues, services	65,808	51,253	222,324	150,066
International Crude Tankers Segment [Member]
Segment Reporting Information [Line Items]
Revenues, services	54,869	49,920	186,715	123,439
Depreciation and amortization	15,079	14,848	44,351	39,961
Loss/(gain) on disposal of vessels and other property	12	17,360	28	23,293
Adjusted income/(loss) from vessel operations	2,722	(4,641)	25,136	(21,863)
Equity in income of affiliated companies	5,031	4,718	14,404	15,002
Investments in and advances to affiliated companies	140,307	149,387	140,307	149,387
Adjusted total assets	1,273,363	1,297,101	1,273,363	1,297,101
Expenditures for vessels and vessel improvements			9,096	133,756
Payments for drydockings			11,945	3,359
International Crude Tankers Segment [Member] \| Time Charter Equivalent Services [Member]
Segment Reporting Information [Line Items]
Revenues, services	49,446	40,348	167,016	103,953
International Product Carriers Segment [Member]
Segment Reporting Information [Line Items]
Revenues, services	16,409	11,006	55,447	46,374
Depreciation and amortization	3,856	4,434	12,268	13,682
Loss/(gain) on disposal of vessels and other property	(1,484)			(6,100)
Adjusted income/(loss) from vessel operations	(579)	(8,560)	4,357	(15,120)
Investments in and advances to affiliated companies	10,933	13,686	10,933	13,686
Adjusted total assets	306,039	348,253	306,039	348,253
Expenditures for vessels and vessel improvements			701	1,459
Payments for drydockings			1,594	609
International Product Carriers Segment [Member] \| Time Charter Equivalent Services [Member]
Segment Reporting Information [Line Items]
Revenues, services	16,362	10,905	55,308	46,113
Other Segments [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	26	35	89	102
Adjusted income/(loss) from vessel operations	(27)	(35)	(110)	600
Equity in income of affiliated companies	3,443	620	10,155	7,498
Investments in and advances to affiliated companies	120,415	112,347	120,415	112,347
Adjusted total assets	$ 120,415	$ 112,347	$ 120,415	$ 112,347

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Amounts paid for drydock costs performed pursuant to regulatory requirements.

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The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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Amount of gain (loss) from the difference between the sale price or salvage price and the book value of an asset that was sold or retired, and gain (loss) from the write down of assets from their carrying value to fair value.

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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The net cash outflow or inflow from purchases, sales and disposals of property, plant and equipment and other productive assets, including intangibles.

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