16.COMMITMENTS AND CONTINGENCIES

Leases

The Company is obligated under various non-cancelable operating leases for land, office space, equipment and site leases that expire at various times through December 2152. In addition, the Company is obligated under various non-cancelable capital leases for vehicles that expire at various times through September 2021.

The annual minimum lease payments under non-cancelable operating (primarily ground or land leases) and capital leases for the next five years as of December 31, 2017 are as follows (in thousands):



For the year ended December 31,	Capital Leases		Operating Leases
2018	$	1,199	$	220,190
2019		654		222,489
2020		226		224,148
2021		31		226,528
2022		—		228,093
Total minimum lease payments		2,110
Less: amount representing interest		(113)
Present value of future payments		1,997
Less: current obligations		(1,147)
Long-term obligations	$	850

Future minimum rental payments under noncancelable ground leases include payments for certain renewal periods at the Company’s option because failure to renew could result in a loss of the applicable tower and related revenue from tenant leases, thereby making it reasonably assured that the Company will renew the lease. The majority of operating leases provide for renewal at varying escalations. Fixed rate escalations have been included in the table disclosed above.

Rent expense for operating leases was $266.4 million, $253.7 million and $239.8 million for the years ended December 31, 2017, 2016 and 2015, respectively. In addition, certain of the Company’s leases include contingent rent provisions which provide for the lessor to receive additional rent upon the attainment of certain tower operating results and/or lease-up. Contingent rent expense for the years ended December 31, 2017, 2016 and 2015 was $26.6 million, $25.0 million and $24.4 million, respectively.

Tenant Leases

The annual minimum tower lease income to be received for tower space and antenna rental under non-cancelable operating leases for the next five years as of December 31, 2017 are as follows:



For the year ended December 31,	(in thousands)
2018	$	1,437,107
2019		1,267,458
2020		1,060,017
2021		803,351
2022		536,685

The Company’s tenant leases provide for annual escalations and multiple renewal periods, at the tenant’s option. The tenant rental payments disclosed in the table above do not assume exercise of any tenant renewal options, however, fixed rate escalations have been included for the current term.

Litigation

The Company is involved in various claims, lawsuits and proceedings arising in the ordinary course of business. While there are uncertainties inherent in the ultimate outcome of such matters and it is impossible to presently determine the ultimate costs that may be incurred, management believes the resolution of such uncertainties and the incurrence of such costs will not have a material adverse effect on the Company’s consolidated financial position, results of operations or liquidity.

Contingent Purchase Obligations

From time to time, the Company agrees to pay additional consideration (or earnouts) for acquisitions if the towers or businesses that are acquired meet or exceed certain performance targets in the one to three years after they have been acquired. Please refer to Note 3.