Long-Term Debt - Net Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Debt Disclosure [Abstract]
Interest expense	$ 11,607	$ 10,435	$ 21,847	$ 23,479
Interest income	(918)	(436)	(1,264)	(880)
Capitalized interest	(4,050)	(2,519)	(8,718)	(4,435)
Net interest expense	$ 6,639	$ 7,480	$ 11,865	$ 18,164