Significant Customers (Details) (Customer concentration risk)	3 Months Ended		6 Months Ended
	Jun. 30, 2012 item	Jun. 30, 2011 item	Jun. 30, 2012 item	Jun. 30, 2011 item
Consolidated Revenue
Significant Customers
Number of customers	3	3	2	3
Consolidated Revenue | Customer one
Significant Customers
Percentage of concentration risk	23.40%	19.20%	24.00%	19.20%
Consolidated Revenue | Customer two
Significant Customers
Percentage of concentration risk	15.70%	13.00%	15.00%	13.00%
Consolidated Revenue | Customer three
Significant Customers
Percentage of concentration risk	10.20%	11.40%		13.00%
Consolidated accounts receivable
Significant Customers
Number of customers			2	3
Consolidated accounts receivable | Customer one
Significant Customers
Percentage of concentration risk			29.40%	14.90%
Consolidated accounts receivable | Customer two
Significant Customers
Percentage of concentration risk			13.40%	12.80%
Consolidated accounts receivable | Customer three
Significant Customers
Percentage of concentration risk				10.10%