Commitments and Contingencies (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Commitments and Contingencies (Textual) [Abstract]
Additional payment if specified financial criteria are attained based on contractual arrangement	$ 925,000
Minimum period of lease including renewal options, operating leases	5 years
Maximum period of lease including renewal options, operating leases	35 years
Total rent expense	55,200,000	51,900,000	46,700,000
Total rental income	920,000	726,000	564,000
Purchase commitments of products and services through 2016	26,200,000
Repayment period of amounts withheld	12 months
Total outstanding holdbacks	1,500,000	1,800,000
Amount paid to sellers for unused portion of holdbacks	$ 1,800,000	$ 3,300,000	$ 5,000,000