Significant Accounting Policies, Cash, Cash Equivalents and Investments (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	$ 65,030	$ 56,350
Gross unrealized gains	1	8
Gross unrealized losses	(25)	(8)
Fair value disclosure	65,006	56,350
Cash [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	14,746	11,116
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value disclosure	14,746	11,116
Money Market Funds [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	17,708	17,235
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value disclosure	17,708	17,235
Certificates of Deposit [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	1,200	1,880
Gross unrealized gains	0	0
Gross unrealized losses	0	(1)
Fair value disclosure	1,200	1,879
Commercial Paper [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	5,749	5,745
Gross unrealized gains	0	1
Gross unrealized losses	0	(1)
Fair value disclosure	5,749	5,745
Corporate notes and bonds [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	24,123	20,172
Gross unrealized gains	1	7
Gross unrealized losses	(25)	(6)
Fair value disclosure	24,099	20,173
US government agencies securities [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	1,504	202
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value disclosure	1,504	202
Cash and cash equivalents [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	34,710	30,853
Gross unrealized gains	0	0
Gross unrealized losses	0	(1)
Fair value disclosure	34,710	30,852
Short-term investments [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	30,320	25,497
Gross unrealized gains	1	8
Gross unrealized losses	(25)	(7)
Fair value disclosure	$ 30,296	$ 25,498