Summary of Significant Accounting Policies (Details) (USD $)	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
Numerator:
Net income (loss) applicable to common stockholders	$ 7,697,000	$ 7,233,000	$ 2,066,000	$ (3,395,000)	$ (2,032,000)	$ (1,384,000)	$ (352,000)	$ (4,432,000)	$ 13,601,000	$ (8,200,000)	$ (18,086,000)
Denominator:
Weighted average common shares outstanding, basic and diluted									85,882,646	85,051,066	84,488,930
Per share:
Net income (loss) per share applicable to common stockholders, basic and diluted	$ 0.09	$ 0.08	$ 0.02	$ (0.04)	$ (0.02)	$ (0.02)	$ 0.00	$ (0.05)	$ 0.16	$ (0.10)	$ (0.21)
Numerator
Net income (loss) applicable to common stockholders	7,697,000	7,233,000	2,066,000	(3,395,000)	(2,032,000)	(1,384,000)	(352,000)	(4,432,000)	13,601,000	(8,200,000)	(18,086,000)
Denominator
Weighted average common shares outstanding									85,882,646	85,051,066	84,488,930
Dilutive securities:
Stock options									89,418
Restricted stock units									342,142
Diluted shares outstanding									$ 86,314,206	$ 85,051,066	$ 84,488,930
Per share:
Net income (loss) per share applicable to common stockholders									$ 0.16	$ (0.10)	$ (0.21)