Condensed Consolidated Statement Of Changes In Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests In Subsidiaries
Total equity, beginning balance at Dec. 31, 2018	$ 853,842	$ 390	$ 1,596,642	$ 474,809	$ (1,366,773)	$ (914)	$ 149,688
Issuance of common stock:
Employee Stock Purchase Plan	1,695				1,695
Exercise of stock options	5,220	1	5,219
Director stock awards	76		76
Restricted stock	0	2	(2)
Purchase of conversion option in convertible debt, net of tax	(115)		(115)
Purchase of treasury shares	(516)				(516)
Amortization of share awards	3,794		3,794
Purchase of subsidiary shares from noncontrolling interests	(106,989)	15	53,814				(160,818)
Distributions to noncontrolling interests	(5,162)						(5,162)
Net income (loss)	35,930			28,691			7,239
Other comprehensive income (loss)	(486)					(486)
Total equity, ending balance at Sep. 30, 2019	812,648	408	1,659,428	519,023	(1,365,594)	(1,400)	783
Total equity, beginning balance at Jun. 30, 2019	908,657	392	1,600,838	512,618	(1,366,432)	(995)	162,236
Issuance of common stock:
Employee Stock Purchase Plan	838				838
Exercise of stock options	3,486	1	3,485
Director stock awards	21		21
Purchase of conversion option in convertible debt, net of tax	(12)		(12)
Amortization of share awards	1,282		1,282
Purchase of subsidiary shares from noncontrolling interests	(106,989)	15	53,814				(160,818)
Distributions to noncontrolling interests	(91)						(91)
Net income (loss)	5,861			6,405			(544)
Other comprehensive income (loss)	(405)					(405)
Total equity, ending balance at Sep. 30, 2019	812,648	408	1,659,428	519,023	(1,365,594)	(1,400)	783
Total equity, beginning balance at Dec. 31, 2019	812,514	408	1,661,002	517,106	(1,365,792)	(998)	788
Issuance of common stock:
Employee Stock Purchase Plan	1,815				1,815
Exercise of stock options	563		563
Director stock awards	55		55
Restricted stock	0	2	(2)
Purchase of treasury shares	(1,944)				(1,944)
Amortization of share awards	4,600		4,600
Distributions to noncontrolling interests	(2)						(2)
Net income (loss)	12,533			12,541			(8)
Other comprehensive income (loss)	(1,781)					(1,781)
Total equity, ending balance at Sep. 30, 2020	828,353	410	1,666,218	529,647	(1,365,921)	(2,779)	778
Total equity, beginning balance at Jun. 30, 2020	822,479	410	1,664,617	526,457	(1,366,787)	(2,998)	780
Issuance of common stock:
Employee Stock Purchase Plan	866				866
Director stock awards	17		17
Amortization of share awards	1,584		1,584
Distributions to noncontrolling interests	(1)						(1)
Net income (loss)	3,189			3,190			(1)
Other comprehensive income (loss)	219					219
Total equity, ending balance at Sep. 30, 2020	$ 828,353	$ 410	$ 1,666,218	$ 529,647	$ (1,365,921)	$ (2,779)	$ 778