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, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income (loss)	$ (94,715)	$ 163,094	$ 51,625	$ (38,697)	$ 68,379	$ 12,928
Weighted-average shares – basic	15,167		15,106		15,159	15,102
Effect of dilutive securities	0		56		109	72
Weighted-average shares – diluted	15,167		15,162		15,268	15,174
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	100