Other Fair Value Information (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term borrowings	$ 436,215	$ 525,842
Long-term debt	7,885,783	7,380,443
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes and loans receivable	579,071	962,938
Short-term borrowings	412,891	525,842
Long-term debt	7,278,827	7,131,587
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes and loans receivable	565,285	958,377
Short-term borrowings	412,891	525,842
Long-term debt	$ 7,678,210	$ 7,221,459