Segment Reporting (Details 1) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Segment Reporting [Abstract]
Assets, Net	[1]	$ 1,429,100	$ 1,344,553	$ 1,027,967
Cash and cash equivalents		104,746	192,032	$ 195,654
Other assets		64,531	164,590
TOTAL ASSETS		$ 1,598,377	$ 1,701,175

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