Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Changes in allowance for doubtful accounts
Balance at beginning of year	$ 300	$ 595	$ 490
Provisions for doubtful accounts	21		113
Charge-offs, net of recoveries	(71)	(295)	(8)
Balance at end of year	$ 250	$ 300	$ 595