Shareholders' Equity Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Mar. 31, 2019		Mar. 31, 2018		Dec. 31, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance	$ 447,355		$ 221,639		$ 221,639
Net income (loss)	(38,697)		10,295
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	(94)	[1]	(2,659)	[2]
All Other Changes	380		989	[3]
As of ending balance	408,944		230,264		447,355
Share-based compensation	1,038		1,576
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance	151		150		150
All Other Changes	0		1
As of ending balance	151		151		151
Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance	197,630		194,123		194,123
All Other Changes	381	[4]	988	[3]
As of ending balance	198,011		195,111		197,630
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance	249,492		27,366		27,366
Net income (loss)	(38,697)		10,295
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	(94)	[1]	(2,659)	[2]
All Other Changes	0		0
As of ending balance	210,701		35,002		249,492
Accumulated Other Comprehensive Income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance	82		0		0
All Other Changes					(1)
As of ending balance	$ 81		$ 0		$ 82
Time Vested Restricted Stock Units [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, Issued	24,657		37,845
Performance Restricted Stock Units [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, Issued	1,495		1,495

[1] 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 $1.6 million during the three months ended March 31, 2018. During the three months ended March 31, 2018, 37,845 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 $1.0 million during the three months ended March 31, 2019. During the three months ended March 31, 2019, 24,657 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.