Retirement Savings Plan (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Savings Plan [Abstract]
Matching contribution amount	$ 1,600,000	$ 1,400,000	$ 500,000
Discretionary contribution amount	$ 0	$ 0	$ 0