Subsequent Events Subsequent Events - Share Repurchase (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Feb. 28, 2019
Subsequent Event [Line Items]
Subsequent Event, Date	Jan. 11, 2019
10b5-1 share repurchase program [Member]
Subsequent Event [Line Items]
Subsequent Event, Date	Feb. 28, 2019
Stock Repurchase Program, Authorized Amount	$ 50
10b5-1 share repurchase program [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Stock Repurchase Program, Authorized Amount		$ 75