Short-Term and Long-Term Debt (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016		Dec. 31, 2015
Debt Disclosure [Abstract]
Short-Term Debt - Principal	$ 16,100,000	[1]	$ 37,900,000	[2]
Short-Term Debt - Unamortized Debt Issuance Costs	(600,000)	[1]	(600,000)	[2]
Short-Term Debt - Total	15,500,000	[1]	37,300,000	[2]
Long-term Debt - Principal	1,563,000,000		1,568,700,000
Long-Term Debt - Unamortized Debt Issuance Costs	(11,700,000)		(12,000,000)
Long-Term Debt - Total	1,551,300,000		1,556,700,000
Total Debt - Principal	1,579,100,000		1,606,600,000
Total Debt - Unamortized Debt Issuance Costs	(12,300,000)		(12,600,000)
Total Debt - Total	1,566,800,000		$ 1,594,000,000
Long-term Debt Issued	$ 0

[1] Consisted of long-term debt due within one year and notes payable.

[2] Consisted of long-term debt due within one year and notes payable.