Earnings (Loss) Per Common Share (Reconciliation of Earnings (loss) Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Numerator (both basic and diluted)
Net loss	$ (14,487)	$ (5,233)	$ (18,152)	$ (11,139)	$ (12,558)	$ (17,227)	$ (20,209)	$ (25,124)	$ (49,011)	$ (75,118)	$ (128,391)
Denominator
Weighted-average shares (denominator for basic earnings (loss) per share)									77,957	77,390	65,452
Dilutive effect of outstanding stock options, restricted stock and restricted stock unit awards									0	0	0
Denominator for diluted earnings (loss) per share									77,957	77,390	65,452
Loss per common share - Basic	$ (0.19)	$ (0.07)	$ (0.23)	$ (0.14)	$ (0.16)	$ (0.22)	$ (0.26)	$ (0.33)	$ (0.63)	$ (0.97)	$ (1.96)
Loss per common share - Diluted	$ (0.19)	$ (0.07)	$ (0.23)	$ (0.14)	$ (0.16)	$ (0.22)	$ (0.26)	$ (0.33)	$ (0.63)	$ (0.97)	$ (1.96)
Stock Compensation Plan [Member]
Denominator
Potentially dilutive securities excluded as anti-dilutive									4,722	5,116	4,953