Marketable Securities (Maturities, at par) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Summary of maturities, at par, of marketable securities
2013	$ 4,057	$ 20,774
2014	18,818	19,944
2015	21,723	18,329
2016	11,690	4,037
2017	6,398
Total	62,686	63,084
Certificates of deposit
Summary of maturities, at par, of marketable securities
2013	965	1,268
2014	1,627	1,627
2015	4,213	4,316
2016	1,501	301
2017	437
Total	8,743	7,512
US Treasury and agency notes
Summary of maturities, at par, of marketable securities
2013	890	6,285
2014	6,787	7,248
2015	5,168	2,633
2016	2,350	11
2017	592
Total	15,787	16,177
Corporate notes
Summary of maturities, at par, of marketable securities
2013	1,752	10,916
2014	6,729	6,729
2015	10,137	9,420
2016	6,604	3,325
2017	5,074
Total	30,296	30,390
Municipal notes
Summary of maturities, at par, of marketable securities
2013	450	2,305
2014	3,675	4,340
2015	2,205	1,960
2016	1,235	400
2017	295
Total	$ 7,860	$ 9,005