Condensed Consolidated Statements of Changes in Shareholders’ Equity - USD ($) $ in Millions	Total	Common Stock	Common Stock Subscribed, Unissued	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interests
Balance at Dec. 31, 2017	$ 761.6	$ 387.7	$ 0.0	$ 619.9	$ (250.1)	$ 4.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	119.4			119.1		0.3
Other comprehensive income (loss)	11.8				11.8
Stock issued	14.9	14.9
Stock purchased	(13.1)	(12.8)				(0.3)
Advance payments	1.0		1.0
Dividends declared	(17.5)			(17.5)
Balance at Sep. 30, 2018	878.9	389.8	1.0	722.3	(238.3)	4.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASC 606, net of tax	0.8			0.8
Balance at Dec. 31, 2018	870.5	428.8	0.0	678.1	(240.3)	3.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	130.4			130.1		0.3
Other comprehensive income (loss)	13.8				13.6	0.2
Stock issued	16.4	15.6				0.8
Stock purchased	(15.7)	(15.3)				(0.4)
Advance payments	1.0		1.0
Dividends declared	(19.3)			(19.3)
Balance at Sep. 30, 2019	$ 997.1	$ 429.1	$ 1.0	$ 788.9	$ (226.7)	$ 4.8