Debt (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Debt Instrument [Line Items]
Principal payments on debt			$ 116,000,000
Cash payments for interest			40,300,000	15,000,000
Amortization of net (loss) gain on treasury lock	1,400,000	1,400,000	2,800,000	2,800,000
Amortization of financing costs	500,000	200,000	900,000	400,000
Book value of fixed rate debt	1,250,000,000		1,250,000,000
Book value of variable rate debt	1,180,000,000		1,180,000,000
Long-term debt (fixed-rate debt), fair value	$ 1,330,000,000		$ 1,330,000,000