Notes Payable (Interest Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Total interest incurred	$ 42,767	$ 31,347	$ 26,314
Interest capitalized	(9,243)	(4,697)	(3,579)
Total interest expense	$ 33,524	$ 26,650	$ 22,735