Net Earnings (Loss) Per Common Share - Computation of Basic and Diluted Net Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Net Earnings (Loss) per Share—Basic:
Average common shares outstanding									33,594	33,124	32,752
Net Loss	$ (18,683)	$ (8,041)	$ (12,717)	$ (13,886)	$ (1,245)	$ (12,026)	$ (16,543)	$ (14,108)	$ (53,327)	$ (43,922)	$ (76,541)
Net earnings per common share	$ (0.56)	$ (0.24)	$ (0.38)	$ (0.42)	$ (0.04)	$ (0.36)	$ (0.50)	$ (0.43)	$ (1.59)	$ (1.33)	$ (2.34)
Diluted
Average common shares outstanding									33,594	33,124	32,752
Stock options and awards									48	419	464
Average common shares assuming dilution									33,642	33,543	33,216
Net Loss	$ (18,683)	$ (8,041)	$ (12,717)	$ (13,886)	$ (1,245)	$ (12,026)	$ (16,543)	$ (14,108)	$ (53,327)	$ (43,922)	$ (76,541)
Net Earnings (loss) per Share - Assuming Dilution (in dollars per share)	$ (0.56)	$ (0.24)	$ (0.38)	$ (0.42)	$ (0.04)	$ (0.36)	$ (0.50)	$ (0.43)	$ (1.59)	$ (1.33)	$ (2.34)