Summary of Significant Accounting Policies (Stock-Based Compensation) (Details)	12 Months Ended
	Dec. 31, 2017
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Stock Options | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Stock Options | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
RSAs | Ratably
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
RSAs | Cliff
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
RSAs | Fourth year of employment
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights (as a percent)	50.00%
RSAs | Fifth year of employment
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights (as a percent)	50.00%
RSAs | Fifth year of employment | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rights (as a percent)	50.00%
RSUs | Ratably
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
RSUs | Cliff | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
RSUs | Cliff | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	5 years