Stockholders' Equity - Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Loss
Dividends declared per common share (in dollars per share)	$ 0.90	$ 0.90	$ 0.90	$ 0.85	$ 2.70	$ 2.55
Aggregated dividend paid	$ 46.3	$ 46.3	$ 46.3
Dividend payable date declared	Sep. 16, 2019	Jun. 18, 2019	Feb. 26, 2019
Common stock Dividend Payable Date	Oct. 15, 2019	Jul. 15, 2019	Apr. 15, 2019
Dividend payable date of record	Sep. 30, 2019	Jun. 28, 2019	Mar. 29, 2019