Cash, cash equivalents, short-term investments, and marketable securities (Details 1) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Schedule of Company's investments
Short-term investments and available for sale securities, Amortized Cost	$ 166,115	$ 20,233
Short-term investments and available for sale securities, Gross Unrealized Gains	156	42
Short-term investments and available for sale securities, Gross Unrealized Losses	205	0
Short-term investments and available for sale securities, Fair Value	166,066	20,275
Short-Term Municipal Bond Fund [Member]
Schedule of Company's investments
Short-term investments and available for sale securities, Amortized Cost	20,436	20,233
Short-term investments and available for sale securities, Gross Unrealized Gains	84	42
Short-term investments and available for sale securities, Gross Unrealized Losses	0	0
Short-term investments and available for sale securities, Fair Value	20,520	20,275
Commercial paper [Member]
Schedule of Company's investments
Short-term investments and available for sale securities, Amortized Cost	13,988
Short-term investments and available for sale securities, Gross Unrealized Gains	0
Short-term investments and available for sale securities, Gross Unrealized Losses	17
Short-term investments and available for sale securities, Fair Value	13,971
Corporate Notes and Bonds [Member]
Schedule of Company's investments
Short-term investments and available for sale securities, Amortized Cost	118,535
Short-term investments and available for sale securities, Gross Unrealized Gains	70
Short-term investments and available for sale securities, Gross Unrealized Losses	184
Short-term investments and available for sale securities, Fair Value	118,421
U.S. Government Agencies [Member]
Schedule of Company's investments
Short-term investments and available for sale securities, Amortized Cost	13,156
Short-term investments and available for sale securities, Gross Unrealized Gains	2
Short-term investments and available for sale securities, Gross Unrealized Losses	4
Short-term investments and available for sale securities, Fair Value	$ 13,154