Stockholders' Equity (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Stock Repurchased	2,700,000
Treasury Stock, Value, Acquired, Cost Method	$ 101.1
Shares Paid for Tax Withholding for Share Based Compensation	16,400
2012 Repurchase Program [Member]
Class of Stock [Line Items]
Maximum number of shares authorized to be repurchased	5,000,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	1,338,689
Stock Repurchased	600,000	0
Treasury Stock, Value, Acquired, Cost Method	$ 42.5