Significant Customers (Details) (Customer concentration risk)	3 Months Ended		9 Months Ended
	Sep. 30, 2012 item	Sep. 30, 2011 item	Sep. 30, 2012 item	Sep. 30, 2011 item
Consolidated Revenue
Significant Customers
Number of customers	3	3	2	3
Consolidated Revenue | Customer one
Significant Customers
Percentage of concentration risk	16.10%	14.40%	21.30%	17.90%
Consolidated Revenue | Customer two
Significant Customers
Percentage of concentration risk	13.10%	13.90%	11.40%	11.40%
Consolidated Revenue | Customer three
Significant Customers
Percentage of concentration risk	10.90%	10.40%		10.40%
Consolidated accounts receivable
Significant Customers
Number of customers			2	3
Consolidated accounts receivable | Customer one
Significant Customers
Percentage of concentration risk			13.00%	15.30%
Consolidated accounts receivable | Customer two
Significant Customers
Percentage of concentration risk			12.00%	14.10%
Consolidated accounts receivable | Customer three
Significant Customers
Percentage of concentration risk				10.40%