Segment Information, Reconciliation of Total Segment Profits to Consolidated Totals (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reconciliation of total segment profits (losses) to the Company's consolidated totals [Abstract]
Net income (loss)	$ 6,903	$ (2,703)	$ (13,649)	$ 26,736
Net loss attributable to non-controlling interest in subsidiaries	(92)	(36)	(238)	(137)
Net income (loss) attributable to controlling interest	6,995	(2,667)	(13,411)	26,873
Reportable Segments [Member]
Reconciliation of total segment profits (losses) to the Company's consolidated totals [Abstract]
Net income (loss)	7,312	(1,479)	(12,474)	27,594
Intersegment Eliminations [Member]
Reconciliation of total segment profits (losses) to the Company's consolidated totals [Abstract]
Net income (loss)	$ (409)	$ (1,224)	$ (1,175)	$ (858)