Marketable Securities (Details 1) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Summary of maturities, at par, of marketable securities
2012	$ 1,966	$ 10,580
2013	22,761	25,276
2014	21,478	20,551
2015	16,572	10,206
2016	2,814	0
Total	65,591	66,613
Certificates of deposit [Member]
Summary of maturities, at par, of marketable securities
2012	249	1,536
2013	1,255	1,255
2014	1,627	1,627
2015	3,059	2,526
2016	301	0
Total	6,491	6,944
U.S. Treasury and agency notes [Member]
Summary of maturities, at par, of marketable securities
2012	287	4,734
2013	7,785	10,285
2014	8,482	5,856
2015	2,633	936
2016	0	0
Total	19,187	21,811
Corporate notes [Member]
Summary of maturities, at par, of marketable securities
2012	895	3,450
2013	11,416	11,231
2014	7,029	8,923
2015	8,920	5,584
2016	2,113	0
Total	30,373	29,188
Municipal notes [Member]
Summary of maturities, at par, of marketable securities
2012	535	860
2013	2,305	2,505
2014	4,340	4,145
2015	1,960	1,160
2016	400	0
Total	$ 9,540	$ 8,670