Interes Expense (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest Expense Debt Abstract
Net interest expense	$ 41,362	$ 47,434	$ 47,561
InterestCostsIncurred	41,362	48,639	48,579
Interest Costs Capitalized Adjustments	$ 0	$ 1,205	$ 1,018