Details of Selected Balance Sheet Accounts

Accounts Receivable



A summary of accounts receivable follows (in thousands):	December 31,
	2018			2017
Accounts receivable, principally trade	$	26,558		$	20,050
Less allowance for doubtful accounts	(430		)	(572		)
Accounts receivable, net	$	26,128		$	19,478

Inventories



A summary of inventories follows (in thousands):	December 31,
	2018			2017
Raw materials and purchased subassemblies	$	20,011		$	20,448
Work-in-process	1,032			1,146
Finished goods	8,111			7,953
Less reserve for excess and obsolete inventories	(15,024		)	(15,039		)
Inventories, net	$	14,130		$	14,508

Property, Plant, Equipment and Seismic Rental Equipment

A summary of property, plant, equipment and seismic rental equipment follows (in thousands):



	December 31,
	2018			2017
Buildings	$	15,707		$	15,822
Machinery and equipment	132,135			145,654
Seismic rental equipment	1,423			1,677
Furniture and fixtures	3,859			3,869
Other	30,104			28,965
Total	183,228			195,987
Less accumulated depreciation	(133,634		)	(143,834		)
Less impairment of long-lived assets	(36,553		)	—
Property, plant, equipment and seismic rental equipment, net	$	13,041		$	52,153

Total depreciation expense, including amortization of assets recorded under capital leases, for 2018, 2017 and 2016 was $7.6 million, $15.2 million and $20.3 million, respectively.

Accrued Expenses



A summary of accrued expenses follows (in thousands):	December 31,
	2018		2017
Compensation, including compensation-related taxes and commissions	$	14,502	$	19,809
Accrued multi-client data library acquisition costs	3,746		5,104
Income tax payable	7,577		1,868
Accrual for loss contingency related to legal proceedings (Footnote 8)	—		3,750
Other	5,586		8,166
Total	$	31,411	$	38,697

Other Long-term Liabilities



A summary of other long-term liabilities follows (in thousands):	December 31,
	2018		2017
Deferred lease liabilities	11,465		12,811
Other	429		1,115
Total	$	11,894	$	13,926