Bonds and Notes Payable - Schedule of TDP Notes Outstanding (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Notes payable	$ 21,356,573	$ 24,668,490
TDP Note 1 [Member]
Line of Credit Facility [Line Items]
Notes payable	$ 12,000
Interest during period	3.38%
TDP Note 2 [Member]
Line of Credit Facility [Line Items]
Notes payable	$ 6,355
Interest during period	3.38%
TDP Note 3 [Member]
Line of Credit Facility [Line Items]
Notes payable	$ 1,743
London Interbank Offered Rate (LIBOR) [Member] | TDP Note 3 [Member]
Line of Credit Facility [Line Items]
Variable interest rate basis	2.00%