Accounts Receivable and Allowance for Doubtful Accounts (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Summary of accounts receivable
Accounts receivable	$ 56,754	$ 54,101
Registration receivable	18,280	14,006
Less: Allowance for doubtful accounts	(1,228)	(1,638)
Accounts receivable, net	$ 73,806	$ 66,469