Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selected quarterly financial data and earnings per share [Abstract]
Revenues	$ 431,339	$ 450,307	$ 484,433	$ 445,168	$ 442,649	$ 467,891	$ 452,417	$ 387,256	$ 1,811,247	$ 1,750,213	$ 1,322,060
Operating (losses) earnings	2,887	303	(643)	5,253	(6,206)	2,239	4,298	1,077
Net (losses) earnings	$ 2,653	$ 640	$ 6	$ 4,908	$ (3,848)	$ 2,035	$ 3,620	$ 1,138	$ 8,207	$ 2,945	$ (482)
Earnings (losses) per share:
Basic earnings (losses) per share (in dollars per share)	$ 0.63	$ 0.15	$ 0	$ 1.16	$ (0.91)	$ 0.48	$ 0.86	$ 0.27	$ 1.94	$ 0.70	$ (0.11)
Diluted net (losses) earnings per share (in dollars per share)	$ 0.63	$ 0.15	$ 0	$ 1.16	$ (0.91)	$ 0.48	$ 0.86	$ 0.27	$ 1.94	$ 0.70	$ (0.11)
Inventory adjustments					$ 7,900					$ 7,900