Cash, Cash Equivalents and Short-Term Investments (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Short term investments classified by security type
Amortized Cost	$ 47,400	$ 51,710
Gross Unrealized Gains	31	47
Gross Unrealized Losses	2	17
Maturities of short-term investments total, Estimated fair value	47,429	51,740	[1]
U.S. Treasury securities [Member]
Short term investments classified by security type
Amortized Cost		3,258
Gross Unrealized Gains		9
Maturities of short-term investments total, Estimated fair value		3,267
Corporate debt securities [Member]
Short term investments classified by security type
Amortized Cost	19,557	22,454
Gross Unrealized Gains	4	6
Gross Unrealized Losses		2
Maturities of short-term investments total, Estimated fair value	19,561	22,458
Municipal securities [Member]
Short term investments classified by security type
Amortized Cost	3,470	4,315
Maturities of short-term investments total, Estimated fair value	3,470	4,315
Government-sponsored enterprise securities [Member]
Short term investments classified by security type
Amortized Cost	22,873	19,033
Gross Unrealized Gains	27	32
Gross Unrealized Losses	1	15
Maturities of short-term investments total, Estimated fair value	22,899	19,050
Bank certificates of deposit [Member]
Short term investments classified by security type
Amortized Cost	1,500	2,650
Gross Unrealized Losses	1
Maturities of short-term investments total, Estimated fair value	$ 1,499	$ 2,650

[1] Derived from December 31, 2011 audited financial statements.