Cash and Cash Equivalents, Short-term Investments and Fair Value of Financial Instruments marketable securities - gain or loss (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Money Market Fund - daily traded value	$ 1
Cash and cash equivalents, Amortized Cost	107,558,000	104,531,000	69,817,000	62,313,000
Cash, cash equiv and S-T-I: Amortized cost	107,558,000	104,531,000
Cash, cash equiv and S-T-I: Gross unrealized gains	0	0
Cash, cash equiv and S-T-I: Gross unrealized losses	0	0
Cash, Cash Equivalents, and Short-term Investments	107,558,000	104,531,000
Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents, Amortized Cost	52,906,000	38,823,000
Cash and cash equivalents - gross unrealized gain	0	0
Cash and cash equivalents - Gross unrealized losses	0	0
Cash and Cash Equivalents, Fair Value Disclosure	52,906,000	38,823,000
Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents, Amortized Cost	54,652,000	65,708,000
Cash and cash equivalents - gross unrealized gain	0	0
Cash and cash equivalents - Gross unrealized losses	0	0
Cash and Cash Equivalents, Fair Value Disclosure	54,652,000	65,708,000
Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash, Cash Equivalents, and Short-term Investments	107,558,000	104,531,000
Cash and Cash Equivalents [Member] | Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	52,906,000	38,823,000
Cash and Cash Equivalents [Member] | Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	$ 54,652,000	$ 65,708,000