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, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	200						100
Net income (loss)	$ (243,413)	$ (94,715)	$ 163,094	$ 54,362	$ 51,625	$ (38,697)	$ (175,034)	$ 67,290
Weighted-average shares – basic	15,183			15,110			15,168	15,105
Effect of dilutive securities	0			50			0	60
Weighted-average shares – diluted	15,183			15,160			15,168	15,165