(15)LEASES

The Company has various operating leases primarily for customer engagement centers, equipment, and office space, which generally contain renewal options. Rent expense under operating leases was approximately $46.3 million, $39.5 million and $37.7 million for the years ended December 31, 2017, 2016 and 2015, respectively.

In 2008, the Company sub-leased one of its customer engagement centers to a third party for the remaining term of the original lease. The sub-lease began on January 1, 2009 and rental income is recognized on a straight-line basis over the term of the sub-lease through 2021. Future minimum sub-lease rental receipts are shown in the table below.

The future minimum rental payments and receipts required under non-cancelable operating leases as of December 31, 2017 are as follows (in thousands):


	Operating		Sub-Lease
	Leases		Income
2018	$	44,177	$	(2,470)
2019		34,528		(2,470)
2020		26,471		(2,470)
2021		20,854		(206)
2022		17,215		—
Thereafter		30,984		—
Total	$	174,229	$	(7,616)

The Company records operating lease expense on a straight-line basis over the life of the lease as described in Note 1. The deferred lease liability as of December 31, 2017 and 2016 was $15.7 million and $15.3 million, respectively.

Asset Retirement Obligations

The Company records asset retirement obligations (“ARO”) for several of its customer engagement center leases. Capitalized costs related to ARO’s are included in Other long-term assets in the accompanying Consolidated Balance Sheets while the ARO liability is included in Other long-term liabilities in the accompanying Consolidated Balance Sheets. Following is a summary of the amounts recorded (in thousands):


	Balance at								Balance at
	December 31,		Additions and						December 31,
	2016		Modifications		Accretion		Settlements		2017

ARO liability total	$	1,861	$	317	$	7	$	(247)	$	1,938


	Balance at								Balance at
	December 31,		Additions and						December 31,
	2015		Modifications		Accretion		Settlements		2016

ARO liability total	$	1,641	$	333	$	15	$	(128)	$	1,861

Increases to ARO result from a new lease agreement or modifications on an ARO from a preexisting lease agreement. Modifications to ARO liabilities and accumulated accretion occur when lease agreements are amended or when assumptions change, such as the rate of inflation. Modifications are accounted for prospectively as changes in estimates. Settlements occur when leased premises are vacated and the actual cost of restoration is paid. Differences between the actual costs of restoration and the balance recorded as ARO liabilities are recognized as gains or losses in the accompanying Consolidated Statements of Comprehensive Income (Loss).