The increase in gross margin was driven primarily by improved results for the natural gas and propane wholesale and marketing subsidiaries , continued growth and colder temperatures on the Delmarva Peninsula and was partially offset by lower gross margin from the propane distribution operations as it incurred $ 1.2 million of non-recurring charges associated with valuing its inventory and its swap agreement to market prices. sales , and an increase in its customer base. respective margin-sharing thresholds earlier in the year .