Shareholders' Equity Rollforward (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance				$ 221,639
Net income (loss)		$ (2,521)	$ 21,329	7,774	$ 49,410
All Other Changes	[1]			(801)
As of ending balance		228,612		228,612
Share-based compensation		900	$ 800	2,451	$ 1,694
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				2,700
Common stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance				150
All Other Changes	[1]			1
As of ending balance		151		151
Paid-in capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance				194,123
All Other Changes	[1]			1,857
As of ending balance		195,980		195,980
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance				27,366
Net income (loss)				7,774
All Other Changes	[1]			(2,659)
As of ending balance		32,481		32,481
Accumulated other comprehensive income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance				0
As of ending balance		$ 0		$ 0
Time Vested Restricted Stock Units [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, Issued		38,115		38,115
Performance Restricted Stock Units [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, Issued		1,495		1,495

[1] 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 time-vested restricted stock units (“RSUs”) and performance restricted stock units (“PRSUs”), net of shares withheld for income taxes, respectively. This also includes a write-off of $2.7 million 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 (see Note 5).