Segment Reporting (Details 1) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Segment Reporting [Abstract]
Assets, Net	[1]	$ 1,548,399	$ 1,550,671	$ 1,424,210
Cash and cash equivalents		69,033	115,081	$ 159,643
Other assets		113,933	46,748
TOTAL ASSETS		$ 1,731,365	$ 1,712,500

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