Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Selected quarterly financial data and earnings per share [Abstract]
Revenues	$ 249,755	$ 266,904	$ 152,286	$ 353,477	$ 431,339	$ 450,307	$ 484,433	$ 445,168	$ 1,022,422	$ 1,811,247	$ 1,750,213
Operating (losses) earnings	5,202	6,056	2,935	(19,940)	2,887	303	(643)	5,253
Net (losses) earnings	$ 5,846	$ 3,073	$ 3,503	$ (11,427)	$ 2,653	$ 640	$ 6	$ 4,908	$ 995	$ 8,207	$ 2,945
Earnings (losses) per share:
Basic earnings (losses) per share (in dollars per share)	$ 1.38	$ 0.72	$ 0.83	$ (2.70)	$ 0.63	$ 0.15	$ 0	$ 1.16	$ 0.23	$ 1.94	$ 0.70
Diluted net (losses) earnings per share (in dollars per share)	$ 1.37	$ 0.72	$ 0.82	$ (2.69)	$ 0.63	$ 0.15	$ 0	$ 1.16	$ 0.23	$ 1.94	$ 0.70
Inventory adjustments	$ (15,000)			$ 24,200	$ 3,700				$ (15,000)	$ 3,700	$ (5,400)