Segment Reporting (Details 1) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Segment Reporting [Abstract]
Assets, Net	[1]	$ 1,424,210	$ 1,344,553	$ 1,023,211
Cash and cash equivalents		159,643	192,032	$ 160,636
Other assets		78,082	164,590
TOTAL ASSETS		$ 1,661,935	$ 1,701,175

[1] Segment assets include receivables, prepaids, inventories, property, plant and equipment, and mineral interest