Long-Term Debt - Debt Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Debt expense recognized	$ 406,341	$ 394,013	$ 389,755
Amortization of deferred financing costs	$ 24,293	$ 20,103	$ 18,625