Stockholders' Deficit (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2012	Dec. 31, 2018
Stockholders' Deficit [Abstract]
Total capital stock, shares authorized	400,000,000
Common stock, shares authorized	300,000,000		300,000,000
Preferred stock, shares authorized	100,000,000		100,000,000
Common stock, par value per share	$ 0.01		$ 0.01
Preferred stock, par value per share	$ 0.01		$ 0.01
Preferred stock, shares outstanding	0
Common stock dividends per share cash paid		$ 0.25
Maximum amount of dividends or stock repurchases permissible under the Credit Facility	$ 100
Amount available for dividend payments, stock repurchases at period end	$ 100