9. Commitments and Contingencies

Leases

We lease office space at our headquarters in Annapolis, Maryland under an operating lease entered into in 2011 and amended in 2013 and 2017 to add additional space. The lease provides for operating expense reimbursements and annual escalations that are amortized over the respective lease terms on a straight-line basis. Lease payments under this lease commenced in 2012 and incremental payments related to the amendments commenced in 2014 and 2017. The lease expires in 2027.

Rent expense was less than $1 million for each of the years ended December 31, 2017, 2016, and 2015, respectively. Future gross minimum lease payments are less than $1 million per year during the remaining term of the lease.

Litigation

The nature of our operations exposes us to the risk of claims and litigation in the normal course of our business. We are not currently subject to any legal proceedings that are probable of having a material adverse effect on our financial position, results of operations or cash flows.