Segment Reporting (Details 1) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting [Abstract]
Assets, Net	[1]	$ 1,344,553	$ 1,045,722	$ 1,012,169
Cash and cash equivalents		192,032	118,312	$ 158,420	$ 240,119
Other assets		164,590	154,875
TOTAL ASSETS		$ 1,701,175	$ 1,318,909

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