Debt (Narrative) (Details) - Long-term Debt, Type [Domain] - USD ($)	3 Months Ended				6 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 01, 2015	Feb. 02, 2015	Dec. 31, 2014	Sep. 08, 2014	Jul. 23, 2014
Debt Instrument [Line Items]
Extinguishment of debt					$ 238,000,000	$ 245,700,000
Loss on debt retirements	$ 0			$ 0	0	$ 8,584,000
Letters of credit outstanding	193,400,000				193,400,000				$ 212,100,000
Notes payable	22,300,000				$ 22,300,000				22,300,000
Debt Instrument, term					6 years
Amount outstanding	119,271,000				$ 119,271,000				140,241,000
Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity											$ 500,000,000
Maximum percent of current credit facility that may be issued in addition					50.00%
Maximum additional issuance					$ 300,000,000
Fair value of amount outstanding	$ 0				0
Revolving Credit Facility Accordion Feature
Debt Instrument [Line Items]
Maximum borrowing capacity											$ 1,000,000,000
Repurchase Agreement | Financial Services
Debt Instrument [Line Items]
Maximum borrowing capacity							$ 150,000,000	$ 99,800,000		$ 150,000,000
Line of Credit Facility, Initiation Date	Jun. 01, 2015	Feb. 02, 2015	Sep. 08, 2014
Line of Credit Facility, Expiration Date	Sep. 07, 2015
Amount outstanding	$ 119,300,000				$ 119,300,000				$ 140,200,000
Maximum
Debt Instrument [Line Items]
Stated interest rate	5.00%				5.00%