Shareholders' Equity Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended							6 Months Ended
	Jun. 30, 2019		Mar. 31, 2019		Jun. 30, 2018	Mar. 31, 2018		Jun. 30, 2019	Jun. 30, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance	$ 408,944		$ 447,355		$ 230,264	$ 221,639		$ 447,355	$ 221,639
Net income (loss)	51,625		(38,697)		(2,521)	10,295		12,928	7,774
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			(94)	[1]		(2,659)	[2]
All Other Changes	985		380		869	989	[3]
As of ending balance	461,554		408,944		228,612	230,264		461,554	228,612
Share-based compensation	1,000				900			2,055	2,451
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance	151		151		151	150		151	150
All Other Changes	0		0		0	1
As of ending balance	151		151		151	151		151	151
Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance	198,011		197,630		195,111	194,123		197,630	194,123
All Other Changes	986	[1]	381	[4]	869	988	[3]
As of ending balance	198,997		198,011		195,980	195,111		198,997	195,980
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance	210,701		249,492		35,002	27,366		249,492	27,366
Net income (loss)	51,625		(38,697)		(2,521)	10,295
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification			(94)	[1]		(2,659)	[2]
All Other Changes	0		0		0	0
As of ending balance	262,326		210,701		32,481	35,002		262,326	32,481
Accumulated Other Comprehensive Income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance	81		82		0	0		82	0
All Other Changes	(1)		(1)
As of ending balance	$ 80		$ 81		$ 0	$ 0		$ 80	$ 0
Time Vested Restricted Stock Units [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, Issued	26,671				38,115			26,671	38,115
Performance Restricted Stock Units [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, Issued	1,495				1,495			1,495	1,495

[1] Attributable to the adoption of ASC Topic 842 as of January 1, 2019 (see Note 9).

[2] ¹ Reflects a write-off for certain accounts receivable attributable to natural gas imbalances accounted for under the entitlements method prior to January 1, 2018, in connection with the adoption of ASC Topic 606, Revenues from Contracts with Customers.

[3] Includes equity-classified share-based compensation of $2.5 million during the six months ended June 30, 2018. During the six months ended June 30, 2018, 38,115 and 1,495 shares of common stock were issued in connection with the vesting of certain RSUs and performance restricted stock units (“PRSUs”), net of shares withheld for income taxes, respectively.

[4] Includes equity-classified share-based compensation of $2.1 million during the six months ended June 30, 2019. During the six months ended June 30, 2019, 26,671 shares of common stock were issued in connection with the vesting of certain time-vested restricted stock units (“RSUs”), net of shares withheld for income taxes.