6	Trade receivables

Trade receivables at December 31, 2018 and 2017, are summarized as follows:

	2018			2017
Maritime
Tugboats	$	26,149		$	14,033
Shipyards		18,897			30,015
Offshore vessels		13,542			21,719
Parcel tankers		12,350			14,773
Bulk Carrier		1,017			-
Others		182			167

Ports and terminals
Shipping agencies		39,877			44,426
Port services		8,843			5,154
Commercial leases		233			434

Logistics, warehousing and other businesses
Warehousing		47,695			52,034
Repair of containers		31,142			27,489
Automotive services		446			689
Other businesses		1,163			-
Total trade receivables		201,536			210,933
Contract assets		68,950			68,014
Allowance for doubtful accounts		(22,303	)		(28,310	)
	$	248,183		$	250,637

All amounts are short-term. The net carrying value of trade accounts receivables is considered a reasonable approximation to fair value.

The movement in the allowance for doubtful accounts is presented below:

	2018			2017
Balance as at January 1	$	28,310		$	35,353
Receivables written off during the year		(468	)		(10,482	)
Disincorporation of TMM DM		-			(9,311	)
Loss allowance (reversed) recognized during the year		(5,539	)		12,750
Balance as at December 31	$	22,303		$	28,310

Note 26 includes disclosures related to credit risk exposures and the analysis related to the allowance for expected credit losses. The impairment loss in 2017 was made by applying the incurred loss analysis in conformity with IAS 39, whereas it applied the expected loss model in accordance with IFRS 9 in the current year.