Summary of Significant Accounting Policies - Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Income tax (benefit), net of refunds	$ 2,186	$ 9,956	$ 6,550
Interest, net of amounts capitalized	189,288	184,462	170,209
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Accrued capital expenditures	130,404	114,855	83,798
Dividends declared but not paid	$ 77,667	$ 72,926	$ 69,363