Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments And Contingencies Disclosure [Abstract]
Rent expense under noncancelable operating leases	$ 1.6	$ 1.5	$ 1.5
Natural gas transportation and treating agreements	through July 2019
Maximum commitments under natural gas transportation and treating agreements	$ 2.4
Contract term related to drilling services	through June 2018
Commitments for contracted drilling services	$ 7.4