Stockholders' Equity (Details) (USD $)	0 Months Ended			12 Months Ended		0 Months Ended
	Mar. 06, 2012	Aug. 24, 2011	Apr. 26, 2007 item	Dec. 31, 2013 item	Dec. 31, 2012	Aug. 01, 2011 1994 Employee Stock Purchase Plan
Capital stock
Common stock, shares authorized				200,000,000	200,000,000
Common stock, shares issued				103,161,000	100,659,000
Common stock, shares outstanding				103,161,000	100,659,000
Common stock, shares issued/sold	9,000,000	6,889,098
Common stock sale price of shares (in dollars per share)		$ 6.65
Gross proceeds from issuance of common stock	$ 202,500,000	$ 45,800,000
Fees and expenses related to offering of common stock	$ 10,500,000	$ 529,000
Common stock shares registered to be issued under share-based payment award plans						600,000
Common stock, par value (in dollars per share)				$ 0.001	$ 0.001	$ 0.001
Preferred stock, shares authorized				5,000,000	5,000,000
Preferred stock, par value (in dollars per share)				$ 1.00	$ 1.00
Number of rights per common stock share issued as dividend			1
Exercise price of preferred stock for each right (in dollars per share)				$ 26.00
Minimum percentage of common stock to be acquired for rights to become exercisable				15.00%
Redemption price per right (in dollars per right)				0.001
Multiplier of the exercise price that the right holder has right to receive in value of acquiring company's common stock				2
Preferred stock, shares issued				0	0
Preferred stock, shares outstanding				0	0