Components of Calculation of Basic and Diluted Earnings Per Share (Details) - USD ($) shares in Thousands, $ 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
Earnings Per Share [Abstract]
Net income (loss)	$ 51,625	$ (38,697)	$ (2,521)		$ 10,295	$ 12,928	$ 7,774
Weighted-average shares – basic	15,106		15,058			15,102	15,050
Effect of dilutive securities	56		0	[1]		72	121
Weighted-average shares – diluted	15,162		15,058			15,174	15,171
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount						100

[1] For the three months ended June 30, 2018, approximately 0.1 million potentially dilutive securities, represented by RSUs and PRSUs, had the effect of being anti-dilutive and were excluded from the calculation of diluted earnings per share.