Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2011

Fair Value Measurements [Abstract]

Summary Of Fair Values, Principal Values And Carrying Values Of The Company's Debt Instruments

	As of December 31, 2011						As of December 31, 2010
	Fair Value		Principal Value		Carrying Value		Fair Value		Principal Value		Carrying Value
	(in millions)
1.875% Convertible Senior Notes due 2013	$	605.2	$	535.0	$	485.0	$	617.4	$	550.0	$	464.0
4.0% Convertible Senior Notes due 2014	$	761.6	$	500.0	$	397.6	$	744.4	$	500.0	$	368.5
8.0% Senior Notes due 2016	$	405.0	$	375.0	$	373.2	$	405.9	$	375.0	$	372.9
8.25% Senior Notes due 2019	$	407.8	$	375.0	$	372.4	$	409.7	$	375.0	$	372.1
4.254% 2010-1 Tower Securities	$	699.0	$	680.0	$	680.0	$	691.9	$	680.0	$	680.0
5.101% 2010-2 Tower Securities	$	579.0	$	550.0	$	550.0	$	556.9	$	550.0	$	550.0
Revolving Credit Facility	$	—	$	—	$	—	$	20.0	$	20.0	$	20.0
Term Loan	$	494.4	$	497.5	$	496.3	$	—	$	—	$	—