Note 15 — Commitments and Contingencies

The Company has entered into certain leases for office space under non-cancellable operating lease agreements that expire on various dates through 2027.

As of December 31, 2017, the approximate aggregate minimum future rental payments required were as follows (in thousands):



2018	$	16,144
2019	16,071
2020	13,727
2021	6,151
2022	3,867
Thereafter	8,106
Total ⁽¹⁾	$	64,066

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(1)	Minimum future rental payments are recorded at their gross amounts and have not been reduced by sublease rentals of $0.7 million for 2018 and $0.5 million for 2019 for approximately 7,000 of aggregate square footage for former Cogent office space in New York and London. The subleases extend through the terms of the existing leases, which both terminate in 2019.

The Company has also entered into various operating leases for office equipment.

Rent expense for leased office space, net of sublease reimbursements, for the years ended December 31, 2017, 2016 and 2015 was approximately $15.0 million, $14.3 million and $16.0 million, respectively.

Diversified financial institutions issued five letters of credit on behalf of the Company to secure office space leases, which totaled $3.9 million and $4.3 million at December 31, 2017 and 2016, respectively. These letters of credit were secured by cash held on deposit. At December 31, 2017 and 2016, no amounts had been drawn under any of the letters of credit. See "Note 4 — Cash and Cash Equivalents".

In addition, the Company has a contingent cash obligation of $18.9 million due the selling unit holders of Cogent if the Earnout is achieved. See "Note 3 — Acquisition" and "Note 8 — Fair Value of Financial Instruments".

The Company is from time to time involved in legal proceedings incidental to the ordinary course of its business. The Company does not believe any such proceedings will have a material adverse effect on its results of operations.