Investments (Details-3) - ATC [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity method investment summarized income statement [Abstract]
Operating revenues	$ 744,371	$ 690,510	$ 721,672
Operating expenses	(373,527)	(358,703)	(346,308)
Other income, net	48	2,405	7,402
Interest expense, net	(110,490)	(110,725)	(110,138)
Earnings before members' income taxes	260,402	223,487	$ 272,628
Equity method investment balance sheet assets [Abstract]
Current assets	84,635	87,250
Noncurrent assets	5,244,220	4,928,793
Total assets	5,328,855	5,016,043
Equity method investment balance sheet liabilities [Abstract]
Current liabilities	502,601	640,040
Long-term debt	2,312,799	2,013,997
Other noncurrent liabilities	298,828	295,281
Members' equity	2,214,627	2,066,725
Total members' equity and liabilities	$ 5,328,855	$ 5,016,043