(5) Commitments and Contingencies

Lease Obligations

The Company leases 319 aircraft, as well as airport facilities, office space, and various other property and equipment under non‑cancelable operating leases which are generally on a long‑term net rent basis where the Company pays taxes, maintenance, insurance and certain other operating expenses applicable to the leased property. The following table summarizes future minimum rental payments required under operating leases that have non‑cancelable lease terms as of December 31, 2017 (in thousands):


2018	$	142,157
2019		104,297
2020		121,119
2021		112,657
2022		75,981
Thereafter		160,621
	$	716,832

The majority of the Company’s leased aircraft are owned and leased through trusts whose sole purpose is to purchase, finance and lease these aircraft to the Company (“Leveraged Lease Agreements”); therefore, they meet the criteria of a variable interest entity. However, since these are single owner trusts in which the Company does not participate, the Company is not considered at risk for losses and is not considered the primary beneficiary. As a result, the Company has not consolidated any of these trusts or any other entities in applying the accounting guidance. The Company’s management believes that the Company’s maximum exposure under these leases is the remaining lease payments.

Total rental expense for non-cancelable aircraft operating leases was approximately $215.8 million, $262.6 million and $273.7 million for the years ended December 31, 2017, 2016 and 2015, respectively. The minimum rental expense for airport station rents was approximately $30.3 million, $31.4 million and $35.1 million for the years ended December 31, 2017, 2016 and 2015, respectively.

Self‑insurance

The Company self‑insures a portion of its potential losses from claims related to workers’ compensation, environmental issues, property damage, medical insurance for employees and general liability. Losses are accrued based on an estimate of the ultimate aggregate liability for claims incurred, using standard industry practices and the Company’s actual experience. Actual results could differ from these estimates.

Legal Matters

The Company is subject to certain legal actions which it considers routine to its business activities. As of December 31, 2017, management believed, after consultation with legal counsel, that the ultimate outcome of such legal matters was not likely to have a material adverse effect on the Company’s financial position, liquidity or results of operations.

Concentration Risk and Significant Customers

The Company requires no collateral from its major airline partners or customers, but monitors the financial condition of its major airline partners. Under the majority of the Company’s code-share agreements, the Company receives weekly payments from its major code-share partners that approximate a significant percentage of the compensation earned for such period. Additionally, the Company provides certain customer service functions at multiple airports for various airlines and the Company maintains an allowance for doubtful accounts receivable based upon expected collectability of all accounts receivable. The Company’s allowance for doubtful accounts totaled $157,000 and $173,000 as of December 31, 2017 and 2016, respectively. For the years ended December 31, 2017, 2016 and 2015, the Company’s contractual relationships with Delta and United combined accounted for approximately 78.8%, 85.4% and 86.9%, respectively of the Company’s total revenues.

Employees Under Collective Bargaining Agreements

As of December 31, 2017, the Company had approximately 16,300 full‑time equivalent employees. Approximately 22.0% of these employees were represented by unions, including the following employee groups. Notwithstanding the completion of the ExpressJet Combination, ExpressJet’s employee groups continue to be represented by those unions who provided representation prior to the ExpressJet Combination.

Accordingly, the following table refers to ExpressJet’s employee groups based upon their union affiliations prior to the ExpressJet Combination.


	Approximate
	Number of
	Active Employees		Status of
Employee Group	Represented	Representatives	Agreement
Atlantic Southeast Pilots	669	Air Line Pilots Association International	Amendable February 2018
Atlantic Southeast Flight Attendants	552	International Association of Machinists and Aerospace Workers	Currently Amendable
Atlantic Southeast Flight Controllers	25	Transport Workers Union of America	Currently Amendable
Atlantic Southeast Mechanics	102	International Brotherhood of Teamsters	Currently Amendable
Atlantic Southeast Stock Clerks	29	International Brotherhood of Teamsters	Currently Amendable
ExpressJet Delaware Pilots	1111	Air Line Pilots Association International	Amendable February 2018
ExpressJet Delaware Flight Attendants	618	International Association of Machinists and Aerospace Workers	Currently Amendable
ExpressJet Delaware Mechanics	418	International Brotherhood of Teamsters	Amendable January 2019
ExpressJet Delaware Dispatchers	22	Transport Workers Union of America	Currently Amendable
ExpressJet Delaware Stock Clerks	42	International Brotherhood of Teamsters	Currently Amendable

In January 2018, the ExpressJet Delaware Mechanics ratified a one-year contract extension to their labor agreement.