Stock-Based Compensation (Assumptions Used in Estimation of Fair Value of Stock Options Granted) (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Black-Scholes fair values of ESPP shares granted	$ 1.92	$ 1.01	$ 2.48	$ 1.00
Risk-free interest rate, minimum	1.33%	0.54%	1.24%	0.54%
Risk-free interest rate, maximum	1.39%	0.96%	2.22%	1.34%
Dividend yield	0.00%	0.00%	0.00%	0.00%
Volatility, minimum	52.87%	55.81%	52.47%	55.81%
Volatility, maximum	53.81%	66.02%	67.93%	73.72%
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	0.11%		0.11%
Risk-free interest rate, maximum	0.14%		0.14%
Dividend yield	0.00%		0.00%
Volatility, minimum	53.80%		53.80%
Volatility, maximum	67.57%		67.57%
Expected forfeiture rate	5.00%		5.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	4 years 1 month 6 days	3 years 11 months 23 days	4 years 14 days	3 years 11 months 23 days
Expected forfeiture rate	0.00%	0.00%	0.00%	0.00%
Minimum [Member] | Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Black-Scholes fair values of ESPP shares granted	$ 0.97		$ 0.97
Expected term (in years)	6 months		6 months
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	4 years 3 months 4 days	4 years 3 months	6 years 11 months 16 days	7 years 18 days
Expected forfeiture rate	23.15%	23.15%	23.15%	23.15%
Maximum [Member] | Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of Black-Scholes fair values of ESPP shares granted	$ 1.79		$ 1.79
Expected term (in years)	1 year		1 year