DETAIL OF SELECTED BALANCE SHEET ACCOUNTS

Accounts Receivable

Accounts receivable is comprised of the following:



	December 31,
	2016			2015
Current:
Accounts receivable	$	69,733		$	67,882
Less allowance for doubtful accounts	(12		)	—
Accounts receivable, net	$	69,721		$	67,882
Noncurrent:
Accounts receivable	37,984			—
Less allowance for doubtful accounts	—			—
Accounts receivable, net, noncurrent	37,984			—

Changes in the allowance for doubtful accounts were as follows:



	Years Ended December 31,
	2016		2015
Beginning balance	$	—	$	—
Charges to expense	12		—
Write-offs	—		—
Ending balance	$	12	$	—

Prepaid Expenses

Prepaid expenses include the following:



	December 31,
	2016		2015
Deposits	1,310		195
Other	667		692
Total prepaid expenses	$	1,977	$	887

Property and Equipment

Property and equipment is comprised of the following:



		December 31,
	Estimated Useful Life	2016			2015
Field operating equipment	3 – 10 years	$	80,780		$	100,001
Vehicles	3 – 5 years	15,905			16,041
Leasehold improvements	2 – 5 years	511			481
Software	3 – 5 years	2,081			1,906
Computer equipment	3 – 5 years	4,005			3,856
Office equipment	3 – 10 years	921			901
		104,203			123,186
Less: accumulated depreciation and amortization		(61,444		)	(61,358		)
Property and equipment, net		$	42,759		$	61,828

Total depreciation and amortization expense for the years ended December 31, 2016 and 2015 was $16,815 and $18,622, respectively, of which $16,410 and $18,137, respectively, was recorded in cost of services and $405 and $485, respectively, was recorded in selling, general and administrative expense.

During the year ended December 31, 2016, the Corporation sold a group of ocean bottom nodes and supporting equipment for aggregate net proceeds of $1,850 which is current reflected in our current accounts receivable and resulted in a pretax loss of $4,580.

Goodwill

Changes in the carrying value of goodwill were as follows:



Balance at December 31, 2014	$	1,977
Foreign currency translation adjustment	(319		)
Balance at December 31, 2015	1,658
Foreign currency translation adjustment	53
Balance at December 31, 2016	$	1,711

There have been no goodwill impairment charges since the 2011 Datum Exploration Ltd. acquisition was initially recorded.

Intangible Assets

Changes in the carrying value of intangible assets and related accumulated amortization were as follows:



	Gross Carrying Amount			Accumulated Amortization			Net Carrying Amount
Balance at December 31, 2014	$	1,491		$	(441	)	$	1,050
Amortization expense	—			(99		)	(99		)
Foreign currency translation adjustment	(162		)	—			(162		)
Balance at December 31, 2015	1,329			(540		)	789
Amortization expense	—			(95		)	(95		)
Foreign currency translation adjustment	27			—			27
Balance at December 31, 2016	$	1,356		$	(635	)	$	721

Intangible assets consist of customer relationships recorded in connection with the 2011 Datum Exploration Ltd. acquisition. The weighted average useful life of customer relationships at December 31, 2016 and 2015 was 13 years.

Future amortization expense is as follows:



2017	$	94
2018	94
2019	94
2020	94
2021	94
Thereafter	251
Total	$	721

Deferred Loan Issuance Costs

Changes in deferred loan issuance costs and related accumulated amortization were as follows:



	Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount
Balance at December 31, 2014	$	852	$	(48	)	$	804
Amortization expense	—		(283		)	(283		)
Balance at December 31, 2015	852		(331		)	521
Senior loan facility issuance costs	30,082		—			30,082
Amortization expense	—		(9,747		)	(9,747		)
Balance at December 31, 2016	$	30,934	$	(10,078	)	$	20,856

Loan issuance costs incurred for the revolving credit agreement signed in November 2014 were capitalized during the year ended December 31, 2014 and are being amortized over three years. Loan issuance costs incurred for the senior loan facility signed in June 2016 were capitalized during the year ended December 31, 2016 and are being amortized over 18 months.

Accrued Liabilities

Accrued liabilities include the following:



	December 31,
	2016		2015
Accrued payroll liabilities	$	7,432	$	5,794
Accrued interest	106		6,463
Other accrued liabilities	5,212		5,561
Total accrued liabilities	$	12,750	$	17,818