Stock-Based Compensation (Narrative) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 2005 Stock Incentive Plan [Member]	Mar. 31, 2014 2005 Stock Incentive Plan [Member] Scenario, Forecast [Member]	Mar. 31, 2014 2005 Stock Incentive Plan [Member] Minimum [Member]	Mar. 31, 2014 2005 Stock Incentive Plan [Member] Maximum [Member]	Mar. 31, 2014 1995 Stock Option Plan [Member]	Mar. 31, 2014 1995 Stock Option Plan [Member] Minimum [Member]	Mar. 31, 2014 1995 Stock Option Plan [Member] Maximum [Member]	Mar. 31, 2014 Employee Stock Purchase Plan [Member]	Apr. 11, 2013 Employee Stock Purchase Plan [Member]	Mar. 31, 2014 Employee Stock Purchase Plan [Member] Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance			22,312,192				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	$ 30,300
Weighted-average remaining contractual term of stock options outstanding	8 years 1 month 6 days
Aggregate intrinsic value of stock options exercisable	15,000
Weighted-average remaining contractual term of stock options exercisable	6 years 6 months
Aggregate intrinsic value of stock options exercised	1,400	100
Unrecognized compensation expense	$ 11,600
Unrecognized compensation expense, recognition period	1 year 8 months 12 days
Increase in shares available for issuance to be approved at the 2014 annual stockholders' meeting				4,000,000