CONSOLIDATED FINANCIAL STATEMENTS' COMPONENTS

Depreciation, Amortization and Accretion

Depreciation, amortization and accretion consisted of the following for the periods stated:



	For the Year Ended December 31,
(Dollars in thousands)	2018			2017			2016
Depreciation
Leasehold improvements	$	232		$	234		$	189
Asset retirement costs	(300		)	(388		)	(277		)
Paging and computer equipment	7,397			8,024			7,974
Furniture, fixtures and vehicles	398			306			294
Total depreciation	7,727			8,176			8,180
Amortization	2,500			2,886			4,160
Accretion	542			562			623
Total depreciation, amortization and accretion expense	$	10,769		$	11,624		$	12,963

Accounts Receivable, net

Accounts receivable was recorded net of an allowance of $1.7 million and $1.1 million for the years ended December 31, 2018 and 2017, respectively. Accounts receivable, net includes $8.7 million and $7.3 million of unbilled receivables for the years ended December 31, 2018 and 2017, respectively. Unbilled receivables are defined as the Company's right to consideration in exchange for goods or services that we have transferred to the customer but have not yet billed for, generally as a result of contractual billing terms. For additional information related to unbilled receivables and adjustments made during the year ended December 31, 2018 please reference Note 1, "Organization and Significant Accounting Policies". The increase in unbilled receivables was primarily due to the adoption of ASC 606 and the acceleration of license revenue for the year ended December 31, 2018.

Property and Equipment, net

Property and equipment, net consisted of the following for the periods stated:



	Useful Life (In Years)	For the Year Ended December 31,
(Dollars in thousands)	Useful Life (In Years)	2018			2017
Leasehold improvements	lease term	$	4,139		$	4,107
Asset retirement costs	1-5	2,021			3,228
Paging and computer equipment	1-5	98,401			103,520
Furniture, fixtures and vehicles	3-5	4,353			4,545
Total property and equipment		108,914			115,400
Accumulated depreciation		(98,560		)	(102,001		)
Total property and equipment, net		$	10,354		$	13,399

For purposes of assessing our asset retirement costs, we completed a review of the estimated useful life of our transmitter assets during the fourth quarter of 2018 (that are part of paging and computer equipment). This review was based on the results of our long-range planning and network rationalization process and indicated that the expected useful life of the last tranche of the transmitter assets was no longer appropriate. As a result of that review, the expected useful life of the final tranche of transmitter assets was extended from 2022 to 2023. This change resulted in a revision of the expected future depreciation expense for the transmitter assets and an immaterial impact to the consolidated financial statements beginning in 2019. We believe these estimates remain reasonable at the present time, but we can give no assurance that changes in technology, customer usage patterns, our financial condition, the economy or other factors would not result in changes to our transmitter decommissioning plans. Any further variations from our estimates could result in a change in the expected useful lives of the underlying transmitter assets and operating results could differ in the future by any difference in depreciation expense. The extension of the depreciable life was accounted for as a change in accounting estimate.

Other Current Liabilities

Other current liabilities consisted of the following for the periods stated:



	December 31,
(Dollars in thousands)	2018		2017
Accrued network costs, asset retirement obligations and other	1,870		2,557
Accrued outside services	$	1,613	$	2,053
Total other current liabilities	$	3,483	$	4,610

Other Non-Current Liabilities

Other non-current liabilities consisted of the following for the periods stated:



	December 31,
(Dollars in thousands)	2018		2017
Asset retirement obligations	$	6,513	$	7,174
Other	1,221		901
Total other non-current liabilities	$	7,734	$	8,075