Shareholders' Equity Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	9 Months Ended
Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance	$ 461,554	$ 447,355	$ 228,612	$ 221,639	$ 447,355	$ 221,639	$ 447,355	$ 221,639
Net income (loss)	54,362	(38,697)	16,276	10,295	51,625	(2,521)	67,290	24,050
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		(94)		(2,659)
All Other Changes	742	380	1,020	989	985	869
As of ending balance	516,658	408,944	245,908	230,264	461,554	228,612	516,658	245,908
Share-based compensation	1,000		1,000				3,101	3,472
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance	151	151	151	150	151	150	151	150
All Other Changes	0	0		1	0	0
As of ending balance	151	151	151	151	151	151	151	151
Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance	198,997	197,630	195,980	194,123	197,630	194,123	197,630	194,123
All Other Changes	742	381	1,020	988	986	869
As of ending balance	199,739	198,011	197,000	195,111	198,997	195,980	199,739	197,000
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance	262,326	249,492	32,481	27,366	249,492	27,366	249,492	27,366
Net income (loss)	54,362	(38,697)	16,276	10,295	51,625	(2,521)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		(94)		(2,659)
All Other Changes	0	0		0	0	0
As of ending balance	316,688	210,701	48,757	35,002	262,326	32,481	316,688	48,757
Accumulated Other Comprehensive Income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
As of beginning balance	80	82	0	0	82	0	82	0
All Other Changes		(1)			(1)
As of ending balance	$ 80	$ 81	$ 0	$ 0	$ 80	$ 0	$ 80	$ 0
Time Vested Restricted Stock Units [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, Issued	42,534		53,411				42,534	53,411
Performance Restricted Stock Units [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares, Issued	1,495		1,495				1,495	1,495

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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