Fair Value of Financial Instruments Fair Value of Long-Term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Total long-term debt, excluding debt issuance costs	$ 1,712,003	$ 1,845,309
Total long-term debt, fair value, excluding debt issuance costs	$ 1,731,271	$ 1,949,638