Stock-Based Compensation (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of stock options exercised	$ 2.1	$ 6.0
Unrecognized compensation expense	$ 49.5
Unrecognized compensation expense, recognition period	1 year 7 months 6 days
2005 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum term of options	10 years
Minimum grant price, percent of common stock fair value	100.00%
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	1,921,846
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized	1,000,000
Employee Stock Ownership Plan (ESOP), Plan Description	The Company adopted an Employee Stock Purchase Plan, as amended (the "ESPP"), which currently authorizes an aggregate of 3,300,000 shares of common stock to be purchased, which aggregate will continue to increase 5% on each anniversary of its adoption up to a maximum of 4,000,000 shares. The Company received approval at its 2016 annual meeting of stockholders to increase the number of shares of common stock available for issuance under the ESPP by 1,000,000 shares. The ESPP allows employees to purchase shares of common stock of the Company at each purchase date through payroll deductions of up to a maximum of 15% of their compensation, at 85% of the lesser of the market price of the shares at the time of purchase or the market price on the beginning date of an option period (or, if later, the date during the option period when the employee was first eligible to participate).
2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	31,000,000
Aggregate intrinsic value of stock options outstanding	$ 79.7
Weighted-average remaining contractual term of stock options outstanding	8 years 1 month 6 days
Aggregate intrinsic value of stock options exercisable	$ 46.7
Weighted-average remaining contractual term of stock options exercisable	6 years 6 months
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized	6,000,000
2015 Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Vesting Period	4 years
2015 Plan [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Options Vesting Period	6 months