Common Stock Repurchases - Narrative (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Common Stock Repurchases (Textual) [Abstract]
Repurchased shares	175,091
Common stock purchased for treasury	$ 9.1
Shares remain available for repurchase	265,449
Repurchase of common stock for employee tax withholding obligations amount, shares	19,237	25,642
Repurchase of common stock for employee tax withholding obligations amount	$ 1.0	$ 1.2