Other Assets and Accrued Liabilities

Prepaid expenses and other, classified as current assets, included the following:



(in thousands)	December 31, 2018		December 31, 2017
Prepaid rent	$	11,245	$	10,519
Prepaid maintenance expenses	3,981		3,062
Interest rate swaps	4,930		2,411
Deferred contract costs	37,957		—
Other	2,049		1,119
Prepaid expenses and other	$	60,162	$	17,111

Deferred contract costs and other include amounts reimbursed to Sprint for commissions and device costs, and commissions and installation costs in the Company’s Cable and Wireline segments. The deferred contract costs increased due to the adoption of Topic 606. Refer to Note 3, Revenue from Contracts with Customers, for additional information.

Accrued liabilities and other, classified as current liabilities, included the following:



(in thousands)	December 31, 2018		December 31, 2017
Sales and property taxes payable	$	4,281	$	3,872
Severance	—		1,028
Asset retirement obligations	582		492
Accrued programming costs	2,886		2,805
Other current liabilities	6,814		5,717
Accrued liabilities and other	$	14,563	$	13,914

The Company's asset retirement obligations (ARO) are included in the balance sheet caption "Asset retirement obligations" and "Accrued liabilities and other". The Company records the fair value of an asset retirement obligation as a liability in the period in which it incurs a legal obligation associated with the retirement and removal of leasehold improvements or equipment. The Company also records a corresponding asset, which is depreciated over the lease term. Subsequent to the initial measurement of the asset retirement obligation, the obligation is adjusted at the end of each period to reflect the passage of time and changes in the estimated future cash flows underlying the obligation. The terms associated with its operating leases, and applicable zoning ordinances of certain jurisdictions, define the Company’s obligations which are estimated and vary based on the size of the towers.

Changes in the liability for asset retirement obligations for the years ended December 31, 2018, 2017 and 2016 are summarized below:



	Years Ended December 31,
(in thousands)	2018			2017			2016
Balance at beginning of year	$	21,703		$	21,507		$	7,266
Liabilities acquired in acquisition	—			—			14,056
Additional liabilities accrued	3,357			2,404			157
Changes to prior estimates	3,504			(1,695		)	—
Payments	(443		)	(1,296		)	(609		)
Accretion expense	1,045			783			637
Balance at end of year	$	29,166		$	21,703		$	21,507