Cash and Cash Equivalents, Short-term Investments and Fair Value of Financial Instruments marketable securities - gain or loss (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Money Market Fund - daily traded value	$ 1.00
Cash and cash equivalents, Amortized Cost	104,531,000	62,313,000	191,762,000	175,635,000
Cash, cash equiv and S-T-I: Amortized cost	104,531,000	62,314,000
Cash, cash equiv and S-T-I: Gross unrealized gains	0	0
Cash, cash equiv and S-T-I: Gross unrealized losses	0	1,000
Cash, Cash Equivalents, and Short-term Investments	104,531,000	62,313,000
Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents, Amortized Cost	38,823,000	23,422,000
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	38,823,000	23,422,000
Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents, Amortized Cost	65,708,000	38,892,000
Cash and cash equivalents - gross unrealized gain		0
Cash and cash equivalents - Gross unrealized losses	0	1,000
Cash and Cash Equivalents, Fair Value Disclosure	65,708,000	38,891,000
Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash, Cash Equivalents, and Short-term Investments	104,531,000	62,313,000
Cash and Cash Equivalents [Member] | Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	38,823,000	23,422,000
Cash and Cash Equivalents [Member] | Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	$ 65,708,000	$ 38,891,000