Earnings (Loss) Per Share - Schedule of Reconciliation of Amounts Used in Basic and Diluted EPS Computation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended					9 Months Ended		12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Basic and Diluted Earnings (Loss) Per Common Share
Net income (loss)	$ 5,971	$ (3,176)	$ (767)	$ 2,366	$ 4,172	$ 16,665	$ 5,771	$ 2,595	$ 17,660
Basic EPS - Weighted average number of common shares outstanding	12,050		12,248			11,936	12,418
Dilutive effect of stock awards	745					407	907
Diluted EPS - Weighted average number of common shares outstanding	12,795		12,248			12,343	13,325
Net earnings (loss) per share: Basic	$ 0.50	$ (0.27)	$ (0.06)	$ 0.19	$ 0.34	$ 1.40	$ 0.46	$ 0.21	$ 1.49
Net earnings (loss) per share: Diluted	$ 0.47	$ (0.27)	$ (0.06)	$ 0.18	$ 0.31	$ 1.35	$ 0.43	$ 0.20	$ 1.41