Condensed Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Treasury Stock	Capital In Excess of Par Value [Member]	Retained earnings (deficit) [Member]	Non-controlling interests in consolidated subsidiaries [Member]
Stockholders' equity, beginning balance at Dec. 31, 2019	$ 1,055,635	$ 10,591		$ 644,152	$ 199,135	$ 201,757
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(1,019,239)	0		0	(986,143)	(33,096)
Activity in employee compensation plans	4,136	113		3,976	0	47
Stockholders' equity, ending balance at Jun. 30, 2020	40,532	10,704		648,128	(787,008)	168,708
Stockholders' equity, beginning balance at Mar. 31, 2020	254,486	10,694		646,543	(571,359)	168,608
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(215,565)	0		0	(215,649)	84
Activity in employee compensation plans	1,611	10		1,585	0	16
Stockholders' equity, ending balance at Jun. 30, 2020	40,532	10,704		648,128	(787,008)	168,708
Stockholders' equity, beginning balance at Dec. 31, 2020	425,593	120	$ 0	197,242	(18,140)	246,371
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(10,706)	0		0	(14,931)	4,225
Activity in employee compensation plans	350	0	0	319	0	31
Distributions to non-controlling interest	(12,344)	0	0	0	0	(12,344)
Repurchase of common stock	(9,048)	0	(9,048)	0	0	0
Stockholders' equity, ending balance at Jun. 30, 2021	393,845	120	(9,048)	197,561	(33,071)	238,283
Stockholders' equity, beginning balance at Mar. 31, 2021	425,092	120	0	197,316	(20,077)	247,733
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(10,115)	0	0	0	(12,994)	2,879
Activity in employee compensation plans	260	0	0	245	0	15
Distributions to non-controlling interest	(12,344)	0	0	0	0	(12,344)
Repurchase of common stock	(9,048)	0	(9,048)	0	0	0
Stockholders' equity, ending balance at Jun. 30, 2021	$ 393,845	$ 120	$ (9,048)	$ 197,561	$ (33,071)	$ 238,283