Segment Information, Reconciliation of Total Segment Profits to Consolidated Totals (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reconciliation of total segment profits to the Company's consolidated totals [Abstract]
Segment profit (loss)	$ 14,165	$ 18,334	$ 29,073	$ 35,317
Net income	14,359	18,141	29,439	35,819
Net loss attributable to non-controlling interest in subsidiaries	(61)	(51)	(101)	(116)
Net income attributable to controlling interest	14,420	18,192	29,540	35,935
Intersegment Recapture (Eliminations) [Member]
Reconciliation of total segment profits to the Company's consolidated totals [Abstract]
Segment profit (loss)	$ 194	$ (193)	$ 366	$ 502