Significant Accounting Policies, Stock-Based Compensation Expense - Weighted-Average Assumptions (Details)	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Employee Stock Options [Member]
Weighted-average assumptions
Risk-free interest rate (in hundredths)	1.60%	1.00%
Dividend yield (in hundredths)	0.00%	0.00%
Volatility (in hundredths)	50.70%	51.40%
Expected life	4 years 7 months 6 days	5 years 1 month 6 days
ESPP [Member]
Weighted-average assumptions
Risk-free interest rate (in hundredths)	0.10%	0.10%
Dividend yield (in hundredths)	0.00%	0.00%
Volatility (in hundredths)	60.60%	62.90%
Expected life	6 months	6 months
Board of Director Stock Options [Member]
Weighted-average assumptions
Risk-free interest rate (in hundredths)	2.20%	2.20%
Dividend yield (in hundredths)	0.00%	0.00%
Volatility (in hundredths)	54.20%	52.70%
Expected life	6 years 10 months 24 days	7 years 2 months 12 days