Long-Term Debt Long-Term Debt - Interest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Interest costs expensed	$ 12,657	$ 13,904	$ 17,914
Interest costs capitalized	0	28	72
Total interest expense and amounts capitalized	$ 12,657	$ 13,932	17,986
Interest expense, building financing arrangement			$ 2,666