Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended			3 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2013 Auction Rate Securities [Member]	Jun. 30, 2012 Auction Rate Securities [Member]	Jun. 30, 2013 Auction Rate Securities [Member]	Jun. 30, 2012 Auction Rate Securities [Member]	Jun. 30, 2013 Maximum [Member]	Jun. 30, 2013 Minimum [Member]	Jun. 30, 2013 Weighted average [Member]	Jun. 30, 2013 U.S. Government Subsidized Securities [Member]	Jun. 30, 2013 Recurring [Member]	Dec. 31, 2012 Recurring [Member]	Jun. 30, 2013 Recurring [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Dec. 31, 2012 Recurring [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Jun. 30, 2013 Recurring [Member] Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2012 Recurring [Member] Significant Other Observable Inputs (Level 2) [Member]	Jun. 30, 2013 Recurring [Member] Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2012 Recurring [Member] Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money Market Funds	$ 70,345												$ 70,345	$ 56,224	$ 70,345	$ 56,224	$ 0	$ 0	$ 0	$ 0
Auction Rate Securities	2,208	3,240										2,208	2,208	3,240	0	0	0	0	2,208	3,240
Investment, total													72,553	59,464	70,345	56,224	0	0	2,208	3,240
Maturity period of US government subsidized securities (in years)	10 years
Redemption period of auction rate securities (in years)									15 years	5 years	6 years
Discount rate for valuing auction rate securities (in hundredths)									2.031%	0.375%	1.23%
Duration of securities subject to temporary impairment, minimum (in months)	12 months
Amount of temporary impairment	192	260
Cash and cash equivalents	79,221	58,838	47,820	70,105
Cash	8,876
Summary of activities in financial instruments with significant Level 3 inputs [Roll Forward]
Balance at beginning of period					3,148	3,240	3,240	3,332
Transfers into Level 3							0	0
Transfers out of Level 3					0	0	0	0
Total gains (losses)
Included in net loss					0	0	0	0
Included in other comprehensive loss					60	0	68	8
Settlements at par					(1,000)	0	(1,100)	(100)
Balance at end of period					2,208	3,240	2,208	3,240
Changes in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period					$ 0	$ 0	$ 0	$ 0