Fair Value Measurements Debt at at Carrying and Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Liabilities:
Total long-term debt	$ 6,396,530	$ 5,920,325
Carrying Value [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value Disclosure	52,500	51,500
Subsidiaries [Member]
Liabilities:
Total long-term debt	4,337,090	4,336,142
Discounted cash flow [Member] | Carrying Value [Member]
Liabilities:
Total long-term debt	6,396,530	5,920,325
Discounted cash flow [Member] | Carrying Value [Member] | Level 2 [Member]
Liabilities:
Long-term debt (fixed-rate), net of discount	6,162,530	5,512,225	[1]
Long-term debt (variable-rate)	234,000	408,100
Debt issuance costs	23,100	24,100
Discounted cash flow [Member] | Fair Value [Member]
Liabilities:
Total long-term debt	7,842,405	7,412,416
Discounted cash flow [Member] | Fair Value [Member] | Level 2 [Member]
Liabilities:
Long-term debt (fixed-rate), net of discount	7,608,405	7,004,316	[1]
Long-term debt (variable-rate)	234,000	408,100
Discounted cash flow [Member] | Subsidiaries [Member] | Carrying Value [Member]
Liabilities:
Total long-term debt	4,337,090	4,336,142
Discounted cash flow [Member] | Subsidiaries [Member] | Carrying Value [Member] | Level 2 [Member]
Liabilities:
Long-term debt (fixed-rate), net of discount	4,337,090	4,336,142	[2]
Debt issuance costs	23,600	24,400
Discounted cash flow [Member] | Subsidiaries [Member] | Fair Value [Member]
Liabilities:
Total long-term debt	5,992,573	5,571,818
Discounted cash flow [Member] | Subsidiaries [Member] | Fair Value [Member] | Level 2 [Member]
Liabilities:
Long-term debt (fixed-rate), net of discount	$ 5,992,573	$ 5,571,818	[2]

[1] ¹ The carrying value includes debt issuances costs of $23.1 million and $24.1 million for June 30, 2020, and December 31, 2019, respectively, which are not included in fair value.

[2] ² The carrying value includes debt issuances costs of $23.6 million and $24.4 million for June 30, 2020, and December 31, 2019, respectively, which are not included in fair value.