Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Shares	Capital in Excess of Par Value	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2018		173,530
Beginning balance at Dec. 31, 2018	$ 1,717,575	$ 17	$ 3,147,925	$ (6,316)	$ (1,424,051)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)		698
Shares issued under equity compensation plans	5,463		5,463
Stock-based compensation	25,385		25,385
Comprehensive loss	(114,912)			4,720	(119,632)
Ending balance (in shares) at Mar. 31, 2019		174,228
Ending balance at Mar. 31, 2019	1,633,511	$ 17	3,178,773	(1,596)	(1,543,683)
Beginning balance (in shares) at Dec. 31, 2018		173,530
Beginning balance at Dec. 31, 2018	$ 1,717,575	$ 17	3,147,925	(6,316)	(1,424,051)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)	2,256
Comprehensive loss	$ (322,099)
Ending balance (in shares) at Sep. 30, 2019		175,786
Ending balance at Sep. 30, 2019	1,488,711	$ 17	3,241,160	88	(1,752,554)
Beginning balance (in shares) at Mar. 31, 2019		174,228
Beginning balance at Mar. 31, 2019	1,633,511	$ 17	3,178,773	(1,596)	(1,543,683)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)		738
Shares issued under equity compensation plans	7,103		7,103
Stock-based compensation	24,522		24,522
Comprehensive loss	(107,981)			2,305	(110,286)
Ending balance (in shares) at Jun. 30, 2019		174,966
Ending balance at Jun. 30, 2019	$ 1,557,155	$ 17	3,210,398	709	(1,653,969)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)	820	820
Shares issued under equity compensation plans	$ 5,882		5,882
Stock-based compensation	24,880		24,880
Comprehensive loss	(99,206)			(621)	(98,585)
Ending balance (in shares) at Sep. 30, 2019		175,786
Ending balance at Sep. 30, 2019	1,488,711	$ 17	3,241,160	88	(1,752,554)
Beginning balance (in shares) at Dec. 31, 2019		176,505
Beginning balance at Dec. 31, 2019	1,405,391	$ 17	3,271,097	(1,005)	(1,864,718)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)		1,358
Shares issued under equity compensation plans	11,347		11,347
Stock-based compensation	24,211		24,211
Comprehensive loss	(144,523)			(5,872)	(138,651)
Ending balance (in shares) at Mar. 31, 2020		177,863
Ending balance at Mar. 31, 2020	1,296,426	$ 17	3,306,655	(6,877)	(2,003,369)
Beginning balance (in shares) at Dec. 31, 2019		176,505
Beginning balance at Dec. 31, 2019	$ 1,405,391	$ 17	3,271,097	(1,005)	(1,864,718)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)	2,889
Comprehensive loss	$ (327,312)
Ending balance (in shares) at Sep. 30, 2020		179,394
Ending balance at Sep. 30, 2020	1,170,981	$ 18	3,363,998	(1,080)	(2,191,955)
Beginning balance (in shares) at Mar. 31, 2020		177,863
Beginning balance at Mar. 31, 2020	1,296,426	$ 17	3,306,655	(6,877)	(2,003,369)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)		947
Shares issued under equity compensation plans	7,826	$ 1	7,825
Stock-based compensation	24,396		24,396
Comprehensive loss	(72,408)			7,592	(80,000)
Ending balance (in shares) at Jun. 30, 2020		178,810
Ending balance at Jun. 30, 2020	$ 1,256,240	$ 18	3,338,876	715	(2,083,369)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)	584	584
Shares issued under equity compensation plans	$ 1,455		1,455
Stock-based compensation	23,667		23,667
Comprehensive loss	(110,381)			(1,795)	(108,586)
Ending balance (in shares) at Sep. 30, 2020		179,394
Ending balance at Sep. 30, 2020	$ 1,170,981	$ 18	$ 3,363,998	$ (1,080)	$ (2,191,955)