Investments in unconsolidated affiliates, generally 50% or less owned partnerships and corporations, are accounted for by the equity method. Under the equity method, the assets and liabilities of the unconsolidated joint venture companies are not consolidated in our consolidated balance sheet.

Investments in, at equity, and advances to unconsolidated joint venture companies were as follows:


	Percentage	December 31,		December 31,
(In thousands)	Ownership	2019		2018
Sonatide Marine, Ltd. (Angola)	49%	$	—	$	—
DTDW Holdings, Ltd. (Nigeria)	40%		—		1,033
GulfMark Marine, Ltd. (Trinidad)	49%		—		6
Investments in, at equity, and advances to unconsolidated companies		$	—	$	1,039

We maintained the following balances with our unconsolidated affiliates as of December 31, 2019 and December 31, 2018:


	December 31,		December 31,
(in thousands)	2019		2018
Due from related parties:
Sonatide (Angola)	$	89,246		109,176
DTDW (Nigeria)		36,726		23,775
		125,972		132,951
Due to related parties:
Sonatide (Angola)	$	31,475		29,347
DTDW (Nigeria)		18,711		5,625
		50,186		34,972
Due from related parties, net of due to related parties	$	75,786		97,979

Amounts due from Sonatide (included in Due from affiliate in the consolidated balance sheets) at December 31, 2019 and December 31, 2018 of approximately $89.0 million and $109.0 million, respectively, represent cash received by Sonatide from customers and due to us, amounts due from customers that are expected to be remitted to us through Sonatide and costs incurred by us on behalf of Sonatide.

	Successor									Predecessor
							Period from			Period from
	Year			Year			August 1, 2017			April 1, 2017
	Ended			Ended			through			through
(In thousands)	December 31, 2019			December 31, 2018			December 31, 2017			July 31, 2017
Due from Sonatide at beginning of year	$	109,176		$	230,315			252,393			262,652
Revenue earned by the company through Sonatide		52,372			56,916			40,303			34,397
Less amounts received from Sonatide		(60,486	)		(76,878	)		(28,264	)		(21,019	)
Less amounts used to offset Due to Sonatide obligations (A)		(10,551	)		(78,993	)		(33,607	)		(21,453	)
Less impairment of due from affiliate		—			(20,083	)		—			—
Other		(1,265	)		(2,101	)		(510	)		(2,184	)
	$	89,246		$	109,176			230,315			252,393

The obligation to us from Sonatide is denominated in U.S. dollars; however, the underlying third-party customer payments to Sonatide were satisfied, in part, in Angolan kwanzas. We and Sonangol, our partner in Sonatide, have had discussions regarding how the net losses from the devaluation of certain Angolan kwanza denominated accounts should be shared. We have been informed that, as part of a broad privatization program, Sonagal intends to seek to divest itself from the Sonatide joint venture in 2020.

Sonatide had approximately $49.2 million of cash on hand, including $8.9 million denominated in Angolan kwanzas at December 31, 2019 plus approximately $8.8 million of net trade accounts receivable, providing approximately $58.0 million

of working capital to satisfy the net due from Sonatide. Given prior discussions with our partner regarding how the net losses from the devaluation of certain Angolan kwanza denominated accounts should be shared, we continue to evaluate our net due from Sonatide balance for potential impairment based on available liquidity held by Sonatide. We determined that a portion of our net due from balance was compromised and in December 2018 we recorded an approximate $20.0 million asset impairment charge. We will continue to monitor the net due from Sonatide balance for possible additional impairment in future periods.

Amounts due to Sonatide (Due to affiliate in the consolidated balance sheets) at December 31, 2019 and 2018 of approximately $31.5 million and $29.3 million, respectively, primarily represents commissions payable and other costs paid by Sonatide on our behalf.

	Successor									Predecessor
							Period from			Period from
							August 1, 2017			April 1, 2017
	Year Ended			Year Ended			through			through
	December 31,			December 31,			December 31,			July 31,
(In thousands)	2019			2018			2017			2017
Due to Sonatide at beginning of year	$	29,347		$	99,448			123,899			132,857
Plus commissions payable to Sonatide		4,937			5,502			3,928			3,330
Plus amounts paid by Sonatide on behalf of the company		9,654			14,778			12,044			9,458
Less commissions paid to Sonatide		(5,961	)		(13,906	)		(5,023	)		—
Less amounts used to offset Due from Sonatide obligations (A)		(10,551	)		(78,993	)		(33,607	)		(21,453	)
Other		4,049			2,518			(1,793	)		(293	)
	$	31,475		$	29,347		$	99,448			123,899

Sonatide’s principal earnings are from the commissions paid by us to the joint venture for company vessels chartered in to Angola. In addition, Sonatide owns four vessels (two of which are currently stacked) that may generate operating income and cash flow.

For the year ended December 31, 2019, our Angolan operation generated vessel revenues of approximately $52.1 million or 10.9% of our consolidated vessel revenues, from an average of approximately 32 company owned vessels that are marketed through the Sonatide joint venture, 13 of which were stacked on average during the year ended December 31, 2019.

For the year ended December 31, 2018, our Angolan operations generated vessel revenues of approximately $59.0 million, or 15%, of our consolidated vessel revenue, from an average of approximately 37 company-owned vessels that are marketed through the Sonatide joint venture (16 of which were stacked on average during the year ended December 31, 2018). For the period from August 1, 2017 through December 31, 2017, our Angolan operations generated vessel revenues of approximately $34.0 million, or 20%, of our consolidated vessel revenue, from an average of approximately 43 company-owned vessels that are marketed through the Sonatide joint venture (16 of which were stacked on average during the period from August 1, 2017 through December 31, 2017). For the period from April 1, 2017 through July 31, 2017, ours Angolan operations generated vessel revenues of approximately $34.0 million, or 23%, of our consolidated vessel revenue, from an average of approximately 50 company-owned vessels that are marketed through the Sonatide joint venture (21 of which were stacked on average during the period from April 1, 2017 through July 31, 2017).