Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013 item	Mar. 31, 2012
Segment Information
Number of business segments in which the entity operates	1
Number of products from which the majority of the entity's product revenues have been derived	1
Segment information
Total revenues	$ 63,094	$ 58,467
United States
Segment information
Total revenues	54,562	53,414
Outside of the United States
Segment information
Total revenues	$ 8,532	$ 5,053

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

No definition available.

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration