Debt - Narrative (Details) - Line of Credit [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Line of Credit Facility Current Borrowing Capacity	$ 300.0
Line of Credit Facility Maximum Borrowing Capacity	$ 400.0
Line Of Credit Maturity Date	Jun. 14, 2019
Line of Credit Facility, Covenant Terms	The Credit Facility has certain financial and other covenants, with the key financial covenant requiring that the Company’s consolidated net debt to adjusted EBITDA ratio cannot exceed 3.50 to 1.
Line of Credit Facility, Covenant Compliance	As of March 31, 2018, and December 31, 2017, the Company’s net debt to adjusted EBITDA ratio was below 1.0 to 1, and the Company was also in compliance with all of its other covenants.
Line of Credit Facility, Amount Outstanding	$ 57.2	$ 48.5