Equity Compensation (401(k) Plan) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($)
Defined Contribution Plan Disclosure [Line Items]
Maximum amount of employees' gross pay the employee may contribute (as a percent)	3.50%
Expenses associated with contribution	$ 0.8
First 1% of employees' salary
Defined Contribution Plan Disclosure [Line Items]
Employer matching contribution (as a percent)	100.00%
Employees' gross pay for which the employer contributes a matching contribution (as a percent)	1.00%
Second 5% of employees' salary
Defined Contribution Plan Disclosure [Line Items]
Employer matching contribution (as a percent)	50.00%
Employees' gross pay for which the employer contributes a matching contribution (as a percent)	5.00%