Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected quarterly financial data and earnings per share [Abstract]
Revenues	$ 442,649	$ 467,891	$ 452,417	$ 387,256	$ 408,460	$ 295,311	$ 315,202	$ 303,087	$ 1,750,213	$ 1,322,060	$ 1,099,540
Operating (losses) earnings	(6,206)	2,239	4,298	1,077	3,757	(1,290)	619	(1,584)
Net (losses) earnings	$ (3,848)	$ 2,035	$ 3,620	$ 1,138	$ 3,693	$ (3,033)	$ (282)	$ (860)	$ 2,945	$ (482)	$ 2,513
Earnings (losses) per share:
Basic net (losses) earnings per share (in dollars per share)	$ (0.91)	$ 0.48	$ 0.86	$ 0.27					$ 0.70	$ (0.11)	$ 0.60
Diluted net (losses) earnings per share (in dollars per share)	$ (0.91)	$ 0.48	$ 0.86	$ 0.27					$ 0.70	$ (0.11)	$ 0.60
Basic and diluted net (losses) earnings per share (in dollars per share)					$ 0.88	$ (0.72)	$ (0.07)	$ (0.20)
Inventory adjustments	$ 7,900								$ 7,900