Segment Reporting (Details 1) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Segment Reporting [Abstract]
Assets, Net	[1]	$ 1,447,904	$ 1,344,553	$ 1,033,387
Cash and cash equivalents		123,539	192,032	$ 200,979
Other assets		64,461	164,590
TOTAL ASSETS		$ 1,635,904	$ 1,701,175

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