Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Percentage of net service revenue
Percentage of net service revenue	100.00%	100.00%	100.00%
Wholly-owned subsidiaries [Member]
Percentage of net service revenue
Percentage of net service revenue	48.10%	49.50%	49.50%
Equity joint ventures [Member]
Percentage of net service revenue
Percentage of net service revenue	49.10%	47.10%	47.40%
License leasing arrangements [Member]
Percentage of net service revenue
Percentage of net service revenue	1.90%	2.40%	1.70%
Management services [Member]
Percentage of net service revenue
Percentage of net service revenue	0.90%	1.00%	1.40%