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, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Schedule of Available-for-sale Securities [Line Items]
Money Market Fund - daily traded value	$ 1.00
Cash and cash equivalents, Amortized Cost	62,313,000	191,762,000	175,635,000	169,230,000
Cash, cash equiv and S-T-I: Amortized cost	62,314,000	199,868,000
Cash, cash equiv and S-T-I: Gross unrealized gains	0	1,000
Cash, cash equiv and S-T-I: Gross unrealized losses	1,000	0
Cash, Cash Equivalents, and Short-term Investments	62,313,000	199,869,000
Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents, Amortized Cost	23,422,000	14,452,000
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	23,422,000	14,452,000
Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents, Amortized Cost	38,892,000	177,310,000
Cash and cash equivalents - gross unrealized gain	0	0
Cash and cash equivalents - Gross unrealized losses	1,000	0
Cash and Cash Equivalents, Fair Value Disclosure	38,891,000	177,310,000
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
A-F-S Securities, Amortized Cost Basis		8,106,000
A-F-S Securities, Gross Unrealized Gains		1,000
A-F-S Securities, Gross Unrealized Losses		0
A-F-S, Fair Value Disclosure		8,107,000
Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash, Cash Equivalents, and Short-term Investments	62,313,000	191,762,000
Cash and Cash Equivalents [Member] | Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	23,422,000	14,452,000
Cash and Cash Equivalents [Member] | Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	38,891,000	177,310,000
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash, Cash Equivalents, and Short-term Investments		8,107,000
Short-term Investments [Member] | US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
A-F-S, Fair Value Disclosure		$ 8,107,000