Impairment Expense	3 Months Ended
Impairment Expense	Mar. 31, 2018
Impairment Of Oil And Gas Properties [Abstract]
Impairment Expense	15. IMPAIRMENT EXPENSE For the three months ended March 31, 2018 and 2017, impairment expenses incurred were approximately $8.2 million and $1.5 million, respectively. We continually monitor the carrying value of our oil and gas properties and make evaluations of their recoverability when circumstances arise that may contribute to impairment. The expense incurred during the first three months of 2018 included approximately $6.9 million of undeveloped leases that expired or are expected to expire without being developed, the majority of which are in Butler County, Pennsylvania, and Warrior North in Ohio. Impairments of proved properties in our Westmoreland County operations totaled approximately $1.2 million during the first three months of 2018. The impairments were identified through an analysis of market conditions and future development plans that were in existence as of each period end related to these properties, which indicated that the carrying value of the assets was not recoverable. The analysis included an evaluation of estimated future cash flows with consideration given to market prices for similar assets and future development plans. Our estimates of future cash flows attributable to our oil and gas properties could decline if commodity prices decline, which may result in our incurrence of additional impairment expense. As of March 31, 2018, we continued to carry the costs of undeveloped properties of approximately $179.3 million on our Consolidated Balance Sheet, which is primarily related to the Marcellus and Utica Shale and for which we currently have development, trade or lease extension plans. The expense incurred during the first three months of 2017 included proved properties of approximately $0.8 million of undeveloped leases that expired or are expected to expire without being developed, the majority of which were in Butler County, Pennsylvania and Warrior North in Ohio. Impairments of proved properties in our Butler County operations totaled approximately $0.7 million during the first three months of 2017

REX ENERGY CORP 10-Q