(5) Commitments and Contingencies 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 Companys actual experience. The Company uses judgment and estimates in determining the ultimate aggregate liabilities for claims incurred in its workers compensation liability. The Company also used significant assumptions in determining the workers compensation liability such as an estimation of loss payment and loss reporting development patterns. At December 31, 2019 and 2018, the Companys accrued workers compensation liability totaled $23.9 million and $42.0 million, respectively. 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, 2019, 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 Companys 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 Companys 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 Companys allowance for doubtful accounts totaled $18,000 and $158,000 as of December 31, 2019 and 2018, respectively. For the years ended December 31, 2019, 2018 and 2017, the Companys contractual relationships with Delta and United combined accounted for approximately 77.6%, 81.4% and 82.9%, respectively of the Companys total revenues. Employees Under Collective Bargaining Agreements As of December 31, 2019, the Company had approximately 13,700 full- time equivalent employees. Although no SkyWest Airlines employees are represented by a national union, certain SkyWest Airline employees are covered under a stable and binding collective bargaining agreement that is administered by employee representatives.