Oil and Gas Producing Activities (Unaudited) - Principal Sources of Changes in the Standardized Measure of Discounted Future Net Flows (Details) $ in Thousands	4 Months Ended
	Apr. 30, 2017 USD ($)
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Roll Forward]
Beginning of year	$ 2,260
Sale of crude oil and natural gas reserves	(2,732)
New field discoveries and extensions, net of future production costs	94
Sales of crude oil and natural gas produced, net of production costs	(476)
Accretion of discount	130
Production rate changes and other	(493)
Net change in income taxes	1,217
End of year	$ 0