Goodwill (Details)	6 Months Ended
	Jun. 30, 2013
Fair value assumptions
Discrete forecast period	5 years
Annual average revenue growth rate (as a percent)	4.00%
Projected growth rates after discrete forecast period (as a percent)	3.00%
Control premium (as a percent)	35.00%
International
Fair value assumptions
Weighted average cost of capital (as a percent)	13.00%
Enterprise value/revenue multiples	0.3
Enterprise value/EBITDA multiples	5.5
Percentage of excess of fair value of goodwill over carrying value	16.00%
North America
Fair value assumptions
Weighted average cost of capital (as a percent)	14.50%
Enterprise value/revenue multiples	0.35
Enterprise value/EBITDA multiples	5
Percentage of excess of fair value of goodwill over carrying value	19.00%