Reserve and Related Financial Data (SMOG) - Unaudited - Principal Sources of Change in Standardized Measure of Discounted Net Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Roll Forward]
Standardized measure of discounted future net cash flows, beginning of the year	$ 443,459	$ 316,468	$ 185,752
Sales, less production costs	(86,492)	(52,278)	(26,711)
Revisions of previous quantity estimates	(41,539)	(22,942)	4,894
Extensions, discoveries, and other additions	69,057	71,668	56,511
Net change in prices and production costs	(99,660)	71,770	30,565
Accretion of discount	51,949	31,713	18,612
Purchase of reserves in place	137,819	148,580	79,190
Divestitures of reserves in place	(5,783)	0	(26,742)
Net change in taxes	(5,739)	(75,369)	(298)
Timing differences and other	2,563	(46,151)	(5,305)
Standardized measure of discounted future net cash flows, end of the year	$ 465,634	$ 443,459	$ 316,468