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	65.8			65.6		0.2
Other comprehensive income (loss)	5.2				5.4	(0.2)
Stock issued	12.0	12.0
Stock purchased	(9.4)	(9.2)				(0.2)
Advance payments	0.5		0.5
Dividends declared	(11.7)			(11.7)
Balance at Jun. 30, 2018	824.8	390.5	0.5	674.6	(244.7)	3.9
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	81.4			81.3		0.1
Other comprehensive income (loss)	11.4				11.2	0.2
Stock issued	12.5	12.5
Stock purchased	(11.1)	(10.8)				(0.3)
Advance payments	0.5		0.5
Dividends declared	(13.0)			(13.0)
Balance at Jun. 30, 2019	$ 952.2	$ 430.5	$ 0.5	$ 746.4	$ (229.1)	$ 3.9