Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Capital in Excess of Par Value [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning balance at Dec. 31, 2019	$ 566,360	$ 1,489	$ (518,030)	$ 4,906,165	$ (3,775,992)	$ (47,272)
Beginning balance, shares at Dec. 31, 2019		148,928,328
Net loss	(345,973)				(345,973)
Other comprehensive income (loss), net of tax	(444)					(444)
Issuance of common stock for employee purchase plan	679	$ 1		678
Issuance of common stock for employee purchase plan, shares		104,331
Issuance of common stock for vesting of restricted stock units		$ 10		(10)
Issuance of common stock for vesting of restricted stock units, shares		950,496
Stock withheld to cover tax withholdings requirements upon vesting of restricted stock units	(48)			(48)
Stock-based compensation expense	3,386			3,386
Ending balance at Mar. 31, 2020	223,960	$ 1,500	(518,030)	4,910,171	(4,121,965)	(47,716)
Ending balance, shares at Mar. 31, 2020		149,983,155
Beginning balance at Dec. 31, 2020	90,463	$ 1,505	(518,030)	4,918,542	(4,255,830)	(55,724)
Beginning balance, shares at Dec. 31, 2020		150,459,034
Net loss	(51,983)				(51,983)
Other comprehensive income (loss), net of tax	6,590					6,590
Issuance of common stock for employee purchase plan	636	$ 2		634
Issuance of common stock for employee purchase plan, shares		239,144
Issuance of common stock for vesting of restricted stock units		$ 13		(13)
Issuance of common stock for vesting of restricted stock units, shares		1,289,209
Stock-based compensation expense	2,682			2,682
Ending balance at Mar. 31, 2021	$ 48,388	$ 1,520	$ (518,030)	$ 4,921,845	$ (4,307,813)	$ (49,134)
Ending balance, shares at Mar. 31, 2021		151,987,387