Cash, Cash Equivalents and Investments (Details Textual) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Cash, Cash Equivalents and Investments [Line Items]
Short-term investments	$ 36,407,000	$ 33,596,000
Cash and Cash Equivalents (Textual) [Abstract]
Cash and cash equivalents maturities	90 days
Investment of cash equivalents are redeemable upon demand using amortized cost method	$ 1.00
Investment in money market funds restricted by investment in short term securities, percentage	100.00%
Cash	13,886,000	13,059,000
Cash equivalents	1,708,000	4,500,000
Cash and cash equivalents in foreign bank	900,000	800,000
Long-term investments	0
Net unrealized gains	1,000,000
Percentage of investment in bond protected by bond default insurance	14.00%
Certificates of deposit	3,600,000	5,100,000
Maximum [Member]
Cash, Cash Equivalents and Investments [Line Items]
Short-term investments, maturities	1 year
Minimum [Member]
Cash, Cash Equivalents and Investments [Line Items]
Short-term investments, maturities	90 days
Pre-refunded municipal bonds [Member]
Cash, Cash Equivalents and Investments [Line Items]
Short-term investments	12,000,000	10,100,000
U.S. government agency bonds [Member]
Cash, Cash Equivalents and Investments [Line Items]
Short-term investments	9,900,000	8,500,000
Corporate debt securities [Member]
Cash, Cash Equivalents and Investments [Line Items]
Short-term investments	$ 10,900,000	$ 9,900,000