Fair Value Measurements and Derivative Instruments (Details) - USD ($) $ in Thousands		Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Assets:
Cash attributed to assets held for sale		$ 14,521		$ 0
Fair Value, Measurements, Nonrecurring | Level 1
Assets:
Cash and cash equivalents	[1],[2]	175,164	$ 121,565
Cash attributed to assets held for sale	[1],[2]	14,521	0
Total Assets	[2]	189,685	121,565
Liabilities:
Long-term debt (including current portion of long-term debt)	[2],[3]	1,202,286	1,536,629
Total Liabilities	[2]	1,202,286	1,536,629
Fair Value, Measurements, Nonrecurring | Level 2
Assets:
Cash and cash equivalents	[1],[4]	0	0
Cash attributed to assets held for sale	[1],[4]	0	0
Total Assets	[4]	0	0
Liabilities:
Long-term debt (including current portion of long-term debt)	[3],[4]	9,324,672	7,358,380
Total Liabilities	[4]	9,324,672	7,358,380
Fair Value, Measurements, Nonrecurring | Level 3
Assets:
Cash and cash equivalents	[1],[5]	0	0
Cash attributed to assets held for sale	[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 | Fair Value, Measurements, Nonrecurring
Assets:
Cash and cash equivalents	[1]	175,164	121,565
Cash attributed to assets held for sale	[1]	14,521	0
Total Assets		189,685	121,565
Liabilities:
Long-term debt (including current portion of long-term debt)	[3]	10,004,487	8,478,473
Total Liabilities		10,004,487	8,478,473
Total Fair Value | Fair Value, Measurements, Nonrecurring
Assets:
Cash and cash equivalents	[1]	175,164	121,565
Cash attributed to assets held for sale	[1]	14,521	0
Total Assets		189,685	121,565
Liabilities:
Long-term debt (including current portion of long-term debt)	[3]	10,526,958	8,895,009
Total Liabilities		$ 10,526,958	$ 8,895,009

[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. 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, 2016 and December 31, 2015.