Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Shares [Member]	Capital in Excess of Par Value [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Beginning Balance at Dec. 31, 2017	$ 87,828	$ 15	$ 2,207,865	$ (2,111)	$ (2,117,941)
Beginning Balance, Shares at Dec. 31, 2017		159,524,000
Shares issued under equity compensation plans	$ 34,406	$ 1	34,405
Shares issued under equity compensation plans, Shares	2,854,816	2,855,000
Stock-based compensation	$ 19,949		19,949
Adoption of new accounting standards	12,577				12,577
Other comprehensive loss	(685)			(685)
Net loss	(95,792)				(95,792)
Ending Balance at Mar. 31, 2018	58,283	$ 16	2,262,219	(2,796)	(2,201,156)
Ending Balance, Shares at Mar. 31, 2018		162,379,000
Beginning Balance at Dec. 31, 2018	1,717,575	$ 17	3,147,925	(6,316)	(1,424,051)
Beginning Balance, Shares at Dec. 31, 2018		173,530,000
Shares issued under equity compensation plans	$ 5,463		5,463
Shares issued under equity compensation plans, Shares	698,000	698,000
Stock-based compensation	$ 25,385		25,385
Other comprehensive loss	3,600			3,600
Net loss	(118,512)				(118,512)
Ending Balance at Mar. 31, 2019	$ 1,633,511	$ 17	$ 3,178,773	$ (2,716)	$ (1,542,563)
Ending Balance, Shares at Mar. 31, 2019		174,228,000