Long-term Debt Narrative (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended			0 Months Ended		6 Months Ended			6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	May 05, 2011 Revolving Credit Facility [Member]	Jun. 30, 2012 Revolving Credit Facility [Member]	Jun. 30, 2012 Credit Facility [Member] Revolving credit facilty, Fourth Amendment [Member]	Jun. 30, 2012 Credit Facility [Member] Revolving credit facilty, Fourth Amendment [Member] Minimum [Member]	Jun. 30, 2012 Credit Facility [Member] Revolving credit facilty, Fourth Amendment [Member] Maximum [Member]	Jun. 30, 2012 Credit Facility [Member] Revolving credit facilty, prior to Fourth Amendment [Member]	Jun. 30, 2012 Credit Facility [Member] Revolving credit facilty, prior to Fourth Amendment [Member] Minimum [Member]	Jun. 30, 2012 Credit Facility [Member] Revolving credit facilty, prior to Fourth Amendment [Member] Maximum [Member]
Debt Instrument [Line Items]
Revolving credit facility							$ 200
Revolving credit facility, potentially additional borrowing capacity							100
Debt instrument, description of variable rate basis								LIBOR or CDOR			LIBOR or CDOR
Revolving credit facility, margin added to variable interest rate									1.75%	2.25%		2.75%	3.50%
Revolving credit facility, amendment fees						0.7
Revolving credit facility, average borrowings	40.5	20.2	32.6	10.1
Revolving credit facility, minimum amount borrowed	0	0	0	0
Revolving credit facility, maximum amount borrowed	91.5	76.1	91.5	76.1
Revolving credit facility, weighted-average interest rate	2.10%	2.30%	2.10%	2.30%
Revolving credit facility and letter of credit, unused facility/participation fees			0.5	0.8
Unamortized debt issuance costs	$ 1.7		$ 1.7		$ 1.9