Marketable Securities (Details 1) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Summary of maturities, at par, of marketable securities
2013	$ 14,790	$ 20,774
2014	18,928	19,944
2015	19,721	18,329
2016	8,717	4,037
2017	1,643
Total	63,799	63,084
Certificates of deposit
Summary of maturities, at par, of marketable securities
2013	1,255	1,268
2014	1,627	1,627
2015	4,213	4,316
2016	1,301	301
2017	0
Total	8,396	7,512
U.S. Treasury and agency notes
Summary of maturities, at par, of marketable securities
2013	5,316	6,285
2014	6,232	7,248
2015	3,573	2,633
2016	2,000	11
2017	18
Total	17,139	16,177
Corporate notes
Summary of maturities, at par, of marketable securities
2013	6,514	10,916
2014	6,729	6,729
2015	9,730	9,420
2016	4,681	3,325
2017	1,625
Total	29,279	30,390
Municipal notes
Summary of maturities, at par, of marketable securities
2013	1,705	2,305
2014	4,340	4,340
2015	2,205	1,960
2016	735	400
2017	0
Total	$ 8,985	$ 9,005