Segment Reporting (Details 1) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016		Dec. 31, 2015
Segment Reporting [Abstract]
Assets, Net	$ 1,091,623	$ 1,122,038	$ 1,117,940	[1]
Cash and cash equivalents	210,033	162,182	$ 173,389		$ 200,714
Other assets	36,094	34,689
TOTAL ASSETS	$ 1,337,750	$ 1,318,909

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