Significant Accounting Policies, Cash, Cash Equivalents and Investments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Cash, Cash Equivalents and Investments [Line Items]
Amortized cost	$ 73,061	$ 73,846
Gross unrealized gains	14	0
Gross unrealized losses	(34)	(53)
Fair value	73,041	73,793
Commercial Paper [Member]
Cash, Cash Equivalents and Investments [Line Items]
Amortized cost	2,996	2,996
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value	2,996	2,996
Corporate Notes and Bonds [Member]
Cash, Cash Equivalents and Investments [Line Items]
Amortized cost	42,158	45,819
Gross unrealized gains	8	0
Gross unrealized losses	(34)	(48)
Fair value	42,132	45,771
US Government Agencies Securities [Member]
Cash, Cash Equivalents and Investments [Line Items]
Amortized cost	7,497	2,000
Gross unrealized gains	4	0
Gross unrealized losses	0	0
Fair value	7,501	2,000
Cash and Cash Equivalents [Member]
Cash, Cash Equivalents and Investments [Line Items]
Amortized cost	16,810	23,354
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value	16,810	23,354
Short-term Investments [Member]
Cash, Cash Equivalents and Investments [Line Items]
Amortized cost	56,251	50,492
Gross unrealized gains	14	0
Gross unrealized losses	(34)	(53)
Fair value	56,231	50,439
Cash [Member]
Cash, Cash Equivalents and Investments [Line Items]
Amortized cost	11,521	9,572
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value	11,521	9,572
Money Market Funds [Member]
Cash, Cash Equivalents and Investments [Line Items]
Amortized cost	5,289	9,859
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value	5,289	9,859
Certificates of Deposits [Member]
Cash, Cash Equivalents and Investments [Line Items]
Amortized cost	3,600	3,600
Gross unrealized gains	2	0
Gross unrealized losses	0	(5)
Fair value	$ 3,602	$ 3,595