Summary of Significant Accounting Policies (Details 5) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of Significant Accounting Policies
Net loss	$ (3,686)	$ (3,967)	$ 3,319	$ (12,416)	$ (18,581)	$ (16,631)	$ (19,562)	$ (22,295)	$ (16,750)	$ (77,069)	$ (81,153)
Weighted average common shares outstanding									21,392	21,189	20,806
Net loss per share:
Basic and diluted (in dollars per share)					$ (0.87)	$ (0.78)	$ (0.92)	$ (1.05)	$ (0.78)	$ (3.64)	$ (3.90)
Anti-dilutive securities excluded from the computation of diluted net income (loss) per share
Anti-dilutive securities (in shares)									2,564	2,486	2,796
Options to purchase shares of common stock
Anti-dilutive securities excluded from the computation of diluted net income (loss) per share
Anti-dilutive securities (in shares)									2,190	1,817	2,411
Shares of common stock issuable upon the vesting of restricted stock units
Anti-dilutive securities excluded from the computation of diluted net income (loss) per share
Anti-dilutive securities (in shares)									374	669	385