Long-Term Debt - Interest Expense And Capitalized Interest (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Interest expense	$ 38,274	$ 45,110	$ 40,024
Interest income	(2,590)	(2,086)	(2,068)
Capitalized interest	(16,906)	(11,785)	(11,042)
Net interest expense	$ 18,778	$ 31,239	$ 26,914