Net Income (Loss) Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Stock Options	Dec. 31, 2012 Stock Options	Dec. 31, 2011 Stock Options	Dec. 31, 2013 Restricted Stock	Dec. 31, 2012 Restricted Stock	Dec. 31, 2011 Restricted Stock	Dec. 31, 2013 Restricted Stock Units (RSUs)	Dec. 31, 2012 Restricted Stock Units (RSUs)	Dec. 31, 2011 Restricted Stock Units (RSUs)	Dec. 31, 2013 Convertible Senior Notes	Dec. 10, 2013 Convertible Senior Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income (loss)	$ (3,412)	$ (8,990)	$ 5,670	$ (9,335)	$ (6,518)	$ (5,857)	$ (6,696)	$ (16,703)	$ (16,068)	$ (35,774)	$ (28,730)
Weighted average shares - basic									62,607	59,811	56,592
Basic income (loss) per share (usd per share)	$ (0.05)	$ (0.14)	$ 0.09	$ (0.16)	$ (0.10)	$ (0.10)	$ (0.11)	$ (0.29)	$ (0.26)	$ (0.60)	$ (0.51)
Securities excluded from calculations of net loss per share because impact would have been anti-dilutive									3,011	3,595	3,767	2,374	2,698	3,127	403	405	640	234	492	0
Convertible notes	$ 67,101				$ 0				$ 67,101	$ 0												$ 86,250
Debt Instrument, Interest Rate, Stated Percentage																					0.00%
Incremental Common Shares Attributable to Conversion of Debt Securities									3,588	0	0