Debt and Other Financing (Narrative) (Details) - USD ($)		1 Months Ended				3 Months Ended				12 Months Ended
	Nov. 30, 2016	Jun. 30, 2018	Dec. 31, 2016	Oct. 31, 2016	Aug. 31, 2016	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2013	Mar. 31, 2009	Mar. 31, 2008	Jun. 30, 2003
Debt Instrument [Line Items]
Short-term debt, interest rate						19.00%				19.00%	23.00%
Obligations under capital leases						$ 2,500,000				$ 2,500,000	$ 4,000,000
Gain (loss) on extinguishment of debt										(700,000)	0	$ 1,100,000
Cash tender offers
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt									$ 3,900,000
Loss on extinguishment, amortization of deferred hedge gain									12,800,000
Debt repurchase, premium paid									5,800,000
Accelerated deferred loss - treasury lock agreements									1,200,000
Cash tender offer, deal costs									1,000,000
Write-off deferred debt issuance cost and discount									$ 900,000
October debt repurchase
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt								$ (1,000,000)
Loss on extinguishment, amortization of deferred hedge gain								6,100,000
Debt repurchase, premium paid				$ 6,200,000				6,200,000
Accelerated deferred loss - treasury lock agreements								400,000
Write-off deferred debt issuance cost and discount								500,000
Accrued interest paid on extinguishment of debt				1,100,000
Debt prepayment
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt								(2,900,000)
Loss on extinguishment, amortization of deferred hedge gain								10,500,000
Accelerated deferred loss - treasury lock agreements								1,000,000
Write-off deferred debt issuance cost and discount								300,000
Accrued interest paid on extinguishment of debt	$ 3,600,000
Make whole premium	12,100,000		$ 12,100,000					12,100,000				12,100,000
December debt repurchase
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt								1,100,000
Write-off deferred debt issuance cost and discount								200,000
Accrued interest paid on extinguishment of debt			300,000
Debt repurchase discount received			1,300,000					1,300,000				1,300,000
Fourth Quarter 2018 Repurchase
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt						2,100,000
Debt repurchase discount received						2,400,000				$ 2,400,000
Payments for debt extinguishment accrued interest						700,000
Write off of debt issuance cost						300,000
2013 Notes
Debt Instrument [Line Items]
Increase in interest rate for every one-notch downgrade of long-term credit ratings below investment grade										0.25%
Maximum aggregate increase in interest rate related to downgrade of long-term credit ratings below investment grade										2.00%
2.375% Notes, due March 2016
Debt Instrument [Line Items]
Principal amount of debt													$ 250,000,000.0
Interest rate, stated percentage													2.375%
4.60% Notes, due March 2020
Debt Instrument [Line Items]
Principal amount of debt													$ 500,000,000.0
Interest rate, stated percentage													4.60%
Repayments of debt					$ 50,100,000
Repurchase amount				40,000,000		23,000,000				$ 23,000,000
Unamortized debt issuance costs						500,000				500,000	900,000
5.00% Notes, due March 2023
Debt Instrument [Line Items]
Principal amount of debt													$ 500,000,000.0
Interest rate, stated percentage													5.00%
Repurchase amount			11,100,000			27,000,000		11,100,000		27,000,000		11,100,000
Unamortized debt issuance costs						1,500,000				1,500,000	1,900,000
6.95% Notes, due March 2043
Debt Instrument [Line Items]
Principal amount of debt													$ 250,000,000.0
Interest rate, stated percentage													6.95%
Repurchase amount			$ 6,200,000					$ 6,200,000				$ 6,200,000
Unamortized debt issuance costs						2,200,000				2,200,000	2,200,000
6.50% Notes, due March 2019
Debt Instrument [Line Items]
Principal amount of debt															$ 350,000,000.0
Interest rate, stated percentage														6.50%	6.50%
Repayments of debt					68,100,000
Gain (loss) on extinguishment of debt							$ (2,900,000)
Repurchase amount				44,000,000
Repayments of long-term debt		$ 237,800,000
Payment for debt extinguishment or debt prepayment cost		6,200,000					6,200,000
Payments for debt extinguishment accrued interest		$ 4,600,000
Write off of debt issuance cost							300,000
Unamortized debt issuance costs						0				$ 0	300,000
5.75% Notes, due March 2018
Debt Instrument [Line Items]
Interest rate, stated percentage															5.75%
Repayments of debt	106,200,000				108,600,000
Repurchase amount				35,200,000
4.20% Notes, due July 2018
Debt Instrument [Line Items]
Interest rate, stated percentage																4.20%
Repayments of debt	$ 132,200,000				73,800,000
Repurchase amount				$ 44,000,000
Notes Payable | All Notes Outstanding, Except 4.20% Notes
Debt Instrument [Line Items]
Minimum required offer to repurchase, percentage of aggregate principal amount										101.00%
7.875% Notes, due August 2022
Debt Instrument [Line Items]
Principal amount of debt					$ 500,000,000.0
Interest rate, stated percentage					7.875%
Unamortized debt issuance costs						$ 5,800,000				$ 5,800,000	$ 7,400,000
Senior Notes
Debt Instrument [Line Items]
Minimum required offer to repurchase, percentage of aggregate principal amount										101.00%
Interest Rate Swap | 6.50% Notes, due March 2019
Debt Instrument [Line Items]
Deferred gain on termination of contract							$ 3,600,000