Carrying Amounts and Fair Values of Financial Instruments for Which the Fair Value Option Was Not Elected (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-Term Notes Payable (Note 12)	$ 0		$ 952,000
Cash and Cash Equivalents	60,475		72,574	$ 176,985	$ 327,420
Long-term debt	$ (2,724,672)		(2,705,718)
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-Term Notes Payable (Note 12)		$ 0	952,000
Long-term debt		(2,752,371)	(2,738,735)
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-Term Notes Payable (Note 12)		0	952,000
Cash and Cash Equivalents		60,475
Long-term debt		$ (2,717,582)	$ (1,808,936)