Fair Value Measurements and Derivative Instruments (Details) - Fair Value, Measurements, Nonrecurring - USD ($) $ in Thousands		Jun. 30, 2017	Dec. 31, 2016
Level 1
Assets:
Cash and cash equivalents	[1],[2]	$ 130,477	$ 132,603
Total Assets	[2]	130,477	132,603
Liabilities:
Long-term debt (including current portion of long-term debt)	[2],[3]	0	0
Total Liabilities	[2]	0	0
Level 2
Assets:
Cash and cash equivalents	[1],[4]	0	0
Total Assets	[4]	0	0
Liabilities:
Long-term debt (including current portion of long-term debt)	[3],[4]	8,540,510	9,859,266
Total Liabilities	[4]	8,540,510	9,859,266
Level 3
Assets:
Cash and cash equivalents	[1],[5]	0	0
Total Assets	[5]	0	0
Liabilities:
Long-term debt (including current portion of long-term debt)	[3],[5]	0	0
Total Liabilities	[5]	0	0
Total Carrying Amount
Assets:
Cash and cash equivalents	[1]	130,477	132,603
Total Assets		130,477	132,603
Liabilities:
Long-term debt (including current portion of long-term debt)	[3]	7,984,221	9,347,051
Total Liabilities		7,984,221	9,347,051
Total Fair Value
Assets:
Cash and cash equivalents	[1]	130,477	132,603
Total Assets		130,477	132,603
Liabilities:
Long-term debt (including current portion of long-term debt)	[3]	8,540,510	9,859,266
Total Liabilities		$ 8,540,510	$ 9,859,266

[1] Consists of cash and marketable securities with original maturities of less than 90 days.

[2] Inputs based on quoted prices (unadjusted) in active markets for identical assets or liabilities that we have the ability to access. Valuation of these items does not entail a significant amount of judgment.

[3] Consists of unsecured revolving credit facilities, senior notes, senior debentures and term loans. This does not include our capital lease obligations.

[4] Inputs other than quoted prices included within Level 1 that are observable for the liability, either directly or indirectly. For unsecured revolving credit facilities and unsecured term loans, fair value is determined utilizing the income valuation approach. This valuation model takes into account the contract terms of our debt such as the debt maturity and the interest rate on the debt. The valuation model also takes into account the creditworthiness of the Company.

[5] Inputs that are unobservable. The Company did not use any Level 3 inputs as of June 30, 2017 and December 31, 2016.