Segment Information, Reconciliation of Total Segment Profits to Consolidated Totals (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reconciliation of total segment profits (losses) to the Company's consolidated totals [Abstract]
Net income (loss)	$ (40,768)	$ 14,359	$ (20,552)	$ 29,439
Net loss attributable to non-controlling interest in subsidiaries	(94)	(61)	(145)	(101)
Net income (loss) attributable to controlling interest	(40,674)	14,420	(20,407)	29,540
Reportable Segments [Member]
Reconciliation of total segment profits (losses) to the Company's consolidated totals [Abstract]
Net income (loss)	(41,113)	14,165	(19,788)	29,073
Intersegment Recapture (Eliminations) [Member]
Reconciliation of total segment profits (losses) to the Company's consolidated totals [Abstract]
Net income (loss)	$ 345	$ 194	$ (764)	$ 366