Components of Calculation of Basic and Diluted Earnings Per Share (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended							9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017		Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income (loss)	$ 16,276	$ (2,521)	$ 10,295	$ (5,947)		$ 21,329	$ 28,081	$ 24,050	$ 43,463
Weighted-average shares – basic	15,062			14,994				15,054	14,993
Effect of dilutive securities	282			0	[1]			224	69
Weighted-average shares – diluted	15,344			14,994				15,278	15,062
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount				100

[1] For the three months ended September 30, 2017, 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.