Long-Term Debt - Net Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Debt Disclosure [Abstract]
Interest expense	$ 10,435	$ 9,751	$ 23,479	$ 18,160
Interest income	(436)	(457)	(880)	(1,107)
Capitalized interest	(2,519)	(4,059)	(4,435)	(7,748)
Net interest expense	$ 7,480	$ 5,235	$ 18,164	$ 9,305