Debt Credit Facility Additional Information (Details) (USD $)	12 Months Ended							6 Months Ended
	Dec. 31, 2011 2007 Senior Secured Credit Facility [Member]	Apr. 02, 2012 2011 Senior Secured Credit Facility [Member]	Aug. 05, 2011 2011 Senior Secured Credit Facility [Member]	Jun. 30, 2012 2011 Senior Secured Credit Facility [Member] Line of Credit [Member]	Apr. 02, 2012 2011 Senior Secured Credit Facility [Member] Line of Credit [Member]	Aug. 05, 2011 2011 Senior Secured Credit Facility [Member] Line of Credit [Member]	Aug. 05, 2011 2011 Senior Secured Credit Facility [Member]	Jun. 30, 2012 U.S. Domestic Subsidiaries [Member]	Jun. 30, 2012 First-Tier Foreign Subsidiaries [Member] Non-voting Stock [Member]	Jun. 30, 2012 Scheduled Quarterly Repayments through June 2013 [Domain]	Jun. 30, 2012 Scheduled Quarterly Repayments September 2013 through June 2014 [Domain]	Jun. 30, 2012 Scheduled Quarterly Repayments September 2014 through June 2016 [Domain]	Jun. 30, 2012 Minimum [Member]	Jun. 30, 2012 Maximum [Member]	Jun. 30, 2012 Maximum [Member] First-Tier Foreign Subsidiaries [Member] Voting Stock [Member]	Jun. 30, 2012 LIBOR interest rate [Member] 2011 Senior Secured Credit Facility [Member]	Jun. 30, 2012 Alternate base rate [Member]	Jun. 30, 2012 Alternate base rate [Member] 2011 Senior Secured Credit Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount							$ 300,000,000
Line of credit facility, maximum borrowing capacity					660,000,000	500,000,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage													0.20%	0.40%
Pledge of Capital Stock								100.00%	100.00%						66.00%
Repayments of Secured Debt										3,800,000	5,600,000	7,500,000
Applicable Interest Rate																1.50%
Debt Instrument, Basis Spread on Variable Rate																1.25%	0.50%	1.00%
Line of credit facility, amount outstanding				170,000,000
Letters of Credit Outstanding, Amount				50,900,000
Line of credit facility, remaining borrowing capacity				439,100,000
Prepaid Debt Fees Noncurrent		897,000	6,600,000
Unamortized prepaid debt fees written-off	$ 2,400,000