Fair Value Measurements Debt at at Carrying and Fair Value (Details) - Discounted cash flow [Member] - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Parent Company [Member] | Carrying Value [Member]
Liabilities:
Long-term Debt, Excluding Current Maturities, Fair Value Disclosure	$ 5,373,567	$ 5,243,608
Parent Company [Member] | Carrying Value [Member] | Level 2 [Member]
Liabilities:
Junior subordinated notes	250,000	250,000
Long-term debt (fixed-rate), net of discount	5,123,567	4,694,608
Long Term Debt (variable rate) net of discount	0	299,000
Parent Company [Member] | Fair Value [Member]
Liabilities:
Long-term Debt, Excluding Current Maturities, Fair Value Disclosure	6,387,015	6,658,789
Parent Company [Member] | Fair Value [Member] | Level 2 [Member]
Liabilities:
Junior subordinated notes	159,346	276,235
Long-term debt (fixed-rate), net of discount	6,227,669	6,083,554
Long Term Debt (variable rate) net of discount	0	299,000
Subsidiaries [Member] | Carrying Value [Member]
Liabilities:
Long-term Debt, Excluding Current Maturities, Fair Value Disclosure	3,786,353	3,763,259
Subsidiaries [Member] | Carrying Value [Member] | Level 2 [Member]
Liabilities:
Junior subordinated notes	250,000	250,000
Long-term debt (fixed-rate), net of discount	3,536,353	3,513,259
Subsidiaries [Member] | Fair Value [Member]
Liabilities:
Long-term Debt, Excluding Current Maturities, Fair Value Disclosure	4,386,245	4,713,708
Subsidiaries [Member] | Fair Value [Member] | Level 2 [Member]
Liabilities:
Junior subordinated notes	159,346	276,235
Long-term debt (fixed-rate), net of discount	$ 4,226,899	$ 4,437,473