Equity Compensation and Employee Benefit Plans (Contributions and Administrative Expenses Under 401(k) Retirement Savings Plan) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
401(k) Plan contributions and administrative expenses	$ 2,357	$ 2,113	$ 2,041