Condensed Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Capital In Excess of Par Value [Member]	Accumulated other comprehensive income (loss) [Member]	Retained earnings [Member]	Non-controlling interests in consolidated subsidiaries [Member]
Cumulative effect adjustment for adoption of ASUs	$ (1,261)	$ 0	$ 0	$ 13	$ (1,274)	$ 0
Stockholders' equity, beginning balance at Dec. 31, 2017	1,345,560	10,280	535,815	63	799,402	0
Net Income (loss)	7,865	0	0	0	7,865	0
Other comprehensive income (loss)	(176)	0	0	(176)	0	0
Total comprehensive income (loss)	7,689
Activity in employee compensation plans	5,312	123	5,189	0	0	0
Stockholders' equity, ending balance at Mar. 31, 2018	1,357,300	10,403	541,004	(100)	805,993	0
Cumulative effect adjustment for adoption of ASUs	174	0	0	0	174	0
Stockholders' equity, beginning balance at Dec. 31, 2018	1,593,444	10,414	628,108	(481)	752,840	202,563
Net Income (loss)	(2,282)	0	0	0	(3,504)	1,222
Other comprehensive income (loss)	24	0	0	24	0	0
Total comprehensive income (loss)	(2,258)
Distributions to non-controlling interest	(918)	0	0	0	0	(918)
Activity in employee compensation plans	5,417	164	5,253	0	0	0
Stockholders' equity, ending balance at Mar. 31, 2019	$ 1,595,859	$ 10,578	$ 633,361	$ (457)	$ 749,510	$ 202,867