Supplemental Financial Data - Oil and Gas Producing Activities (unaudited) (Details 6) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Principal Sources of Change in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Abstract]
Standardized measure of discounted future net cash flows, beginning of year	$ 392,068	$ 57,082
Sales of oil and gas, net of production costs and taxes	(49,746)	(25,681)
Price revisions	(158,799)	133,789
Extensions, discoveries and improved recovery, less related costs	10,822
Changes in estimated future development costs	(3,041)	(32,711)
Development costs incurred during the period	6,685	926
Quantity revisions	5,565	(23,484)
Accretion of discount	39,207	5,708
Net changes in future income taxes	39,929	(89,117)
Purchases of reserves-in-place		391,877
Sales of reserves-in-place	(4,004)
Changes in production rate timing and other	(6,838)	(26,321)
Standardized measure of discounted future net cash flows, end of year	$ 271,848	$ 392,068