Fair Value Measurements and Derivative Instruments (Details) - Fair Value, Measurements, Nonrecurring - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Level 1
Assets:
Cash and cash equivalents	$ 132,603	$ 121,565
Total Assets	132,603	121,565
Liabilities:
Long-term debt (including current portion of long-term debt)	0	0
Total Liabilities	0	0
Level 2
Assets:
Cash and cash equivalents	0	0
Total Assets	0	0
Liabilities:
Long-term debt (including current portion of long-term debt)	9,859,266	8,895,009
Total Liabilities	9,859,266	8,895,009
Level 3
Assets:
Cash and cash equivalents	0	0
Total Assets	0	0
Liabilities:
Long-term debt (including current portion of long-term debt)	0	0
Total Liabilities	0	0
Total Carrying Amount
Assets:
Cash and cash equivalents	132,603	121,565
Total Assets	132,603	121,565
Liabilities:
Long-term debt (including current portion of long-term debt)	9,347,051	8,478,473
Total Liabilities	9,347,051	8,478,473
Total Fair Value
Assets:
Cash and cash equivalents	132,603	121,565
Total Assets	132,603	121,565
Liabilities:
Long-term debt (including current portion of long-term debt)	9,859,266	8,895,009
Total Liabilities	$ 9,859,266	$ 8,895,009