Stockholders' Equity (Summary of Stock Option Activity) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Shares
Outstanding at December 31, 2014			4,077,074
Aggregate Intrinsic Value
Exercised	$ 7,104	$ 8,594
Employee Stock Option [Member] | Stock Compensation Plan [Member]
Shares
Outstanding at December 31, 2013			3,060,583
Granted			2,080,148
Exercised			(210,735)
Canceled			(852,922)
Outstanding at December 31, 2014			4,077,074
Exercisable at December 31, 2014			2,001,911
Vested and expected to vest at December 31, 2014			3,518,464	[1]
Weighted-Average Exercise Price
Outstanding at December 31, 2013			$ 6.76
Granted			$ 8.07
Exercised			$ 2.84
Canceled			$ 9.67
Outstanding at December 31, 2014			$ 7.02
Exercisable at December 31, 2014			$ 5.50
Vested and expected to vest at December 31, 2014			$ 6.85	[1]
Weighted-Average Remaining Contractual Term
Outstanding at December 31, 2014			6 years 11 months 23 days
Exercisable at December 31, 2014			5 years 1 month 20 days
Vested and expected to vest at December 31, 2014			6 years 8 months 5 days	[1]
Aggregate Intrinsic Value
Exercised			1,499	[2]
Outstanding at December 31, 2014			8,259	[2]
Exercisable at December 31, 2014			6,630	[2]
Vested and expected to vest at December 31, 2014			$ 7,745	[1],[2]
Estimated per share fair value of common stock			$ 7.78

[1] This represents the number of vested options as of December 31, 2014 plus the number of unvested options expected to vest as of December 31, 2014, based on the unvested options outstanding at December 31, 2014 and adjusted for the estimated forfeiture rate.

[2] The aggregate intrinsic value was calculated based on the positive difference between the estimated fair value of the Company's common stock on December 31, 2014 of $7.78 per share, or the date of exercise, as appropriate, and the exercise price of the underlying options.