Segment Reporting (Details 1) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
Segment Reporting [Abstract]
Assets, Net	$ 1,122,038	$ 1,103,310	[1]	$ 1,075,259
Cash and cash equivalents	162,182	200,714		$ 270,861	$ 206,690
Other assets	34,689	28,465
TOTAL ASSETS	$ 1,318,909	$ 1,332,489

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