Debt Debt (Schedule of Interest Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Interest Expense [Abstract]
Interest expense	$ 40,385	$ 36,197	$ 30,094
Amortization of debt issuance costs and bond discount	2,627	3,928	4,497
Unamortized debt premium written off as a result of debt payoff	(353)	18	(18)
Capitalized interest	(510)	(549)	(357)
Loss on extinguishment of debt	(2,214)	0	0
Charges taken on restructuring credit facility	583	0	0
Debt issuance costs expensed due to credit facility modifications	3,592	3,514	3,413
Total interest expense	$ 46,324	$ 43,108	$ 37,629