Stock-Based Compensation (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Non-employees [Member]	Jun. 30, 2013 Maximum [Member] Non-employees [Member]	Jun. 30, 2014 2005 Stock Incentive Plan [Member]	Jun. 30, 2014 2005 Stock Incentive Plan [Member] Minimum [Member]	Jun. 30, 2014 2005 Stock Incentive Plan [Member] Maximum [Member]	Jun. 30, 2014 1995 Stock Option Plan [Member]	Jun. 30, 2014 1995 Stock Option Plan [Member] Minimum [Member]	Jun. 30, 2014 1995 Stock Option Plan [Member] Maximum [Member]	Jun. 30, 2014 Employee Stock Purchase Plan [Member]	Apr. 11, 2013 Employee Stock Purchase Plan [Member]	Jun. 30, 2014 Employee Stock Purchase Plan [Member] Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance							26,312,192			5,746,468			1,811,176	2,000,000	3,000,000
Maximum term of options							10 years			10 years
Minimum grant price, percent of common stock fair value							100.00%			100.00%
Exercise period								6 months	4 years		6 months	4 years
Aggregate intrinsic value of stock options outstanding	$ 31,100,000		$ 31,100,000
Weighted-average remaining contractual term of stock options outstanding			8 years
Aggregate intrinsic value of stock options exercisable	16,500,000		16,500,000
Weighted-average remaining contractual term of stock options exercisable			6 years 4 months 24 days
Aggregate intrinsic value of stock options exercised			1,700,000	100,000
Unrecognized compensation expense	13,300,000		13,300,000
Unrecognized compensation expense, recognition period			1 year 7 months 6 days
Increase in shares available for issuance approved at the 2014 annual stockholders' meeting							4,000,000
Stock-based compensation expense	$ 1,852,000	$ 638,000	$ 2,892,000	$ 1,121,000	$ 300,000	$ 100,000							$ 300,000