Significant Accounting Policies, Cash, Cash Equivalents and Investments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	$ 68,468	$ 56,350
Gross unrealized gains	4	8
Gross unrealized losses	(22)	(8)
Fair value disclosure	68,450	56,350
Cash [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	13,244	11,116
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value disclosure	13,244	11,116
Money Market Funds [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	15,756	17,235
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value disclosure	15,756	17,235
Certificates of Deposit [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	3,329	1,880
Gross unrealized gains	0	0
Gross unrealized losses	(1)	(1)
Fair value disclosure	3,328	1,879
Commercial Paper [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	12,996	5,745
Gross unrealized gains	0	1
Gross unrealized losses	(1)	(1)
Fair value disclosure	12,995	5,745
Corporate notes and bonds [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	23,143	20,172
Gross unrealized gains	4	7
Gross unrealized losses	(20)	(6)
Fair value disclosure	23,127	20,173
US government agencies securities [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost		202
Gross unrealized gains		0
Gross unrealized losses		0
Fair value disclosure		202
Cash and cash equivalents [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	30,623	30,853
Gross unrealized gains	0	0
Gross unrealized losses	(1)	(1)
Fair value disclosure	30,622	30,852
Short-term investments [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	37,845	25,497
Gross unrealized gains	4	8
Gross unrealized losses	(21)	(7)
Fair value disclosure	$ 37,828	$ 25,498