Income Taxes - Balance Sheet Location (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosures [Line Items]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ 0	$ 117,185	$ 0
Non-current deferred taxes	789,297	746,868
Total net deferred tax liabilities	789,297	746,868
Subsidiaries [Member]
Income Tax Disclosures [Line Items]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	0	36,328	0
Deferred Tax Assets, Regulatory Assets and Liabilities	(1,012,300)		$ (71,500)
Non-current deferred taxes	926,403	869,473
Total net deferred tax liabilities	926,403	$ 869,473
ARAM [Member]
Income Tax Disclosures [Line Items]
Deferred Other Tax Expense (Benefit)	$ 29,800