Condensed Consolidated Statements Of Changes in Shareholders’ Equity - USD ($) $ in Millions	Common Stock	Common Stock Subscribed, Unissued	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interests	Total
Balance at Dec. 31, 2018	$ 428.8		$ 678.1	$ (240.3)	$ 3.9	$ 870.5
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income			34.3		0.1	34.4
Other comprehensive income (loss)				5.7	0.1	5.8
Stock issued	8.8					8.8
Stock purchased	(5.5)				(0.3)	(5.8)
Advance payments		$ 1.1				1.1
Dividends declared			(6.5)			(6.5)
Balance at Mar. 31, 2019	432.1	1.1	705.9	(234.6)	3.8	908.3
Balance at Dec. 31, 2018	428.8		678.1	(240.3)	3.9	870.5
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income						130.4
Other comprehensive income (loss)						13.8
Balance at Sep. 30, 2019	429.1	1.0	788.9	(226.7)	4.8	997.1
Balance at Mar. 31, 2019	432.1	1.1	705.9	(234.6)	3.8	908.3
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income			47.0			47.0
Other comprehensive income (loss)				5.5	0.1	5.6
Stock issued	3.7					3.7
Stock purchased	(5.3)					(5.3)
Advance payments		(0.6)				(0.6)
Dividends declared			(6.5)			(6.5)
Balance at Jun. 30, 2019	430.5	0.5	746.4	(229.1)	3.9	952.2
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income			48.8		0.2	49.0
Other comprehensive income (loss)				2.4		2.4
Stock issued	3.1				0.8	3.9
Stock purchased	(4.5)				(0.1)	(4.6)
Advance payments		0.5				0.5
Dividends declared			(6.3)			(6.3)
Balance at Sep. 30, 2019	429.1	1.0	788.9	(226.7)	4.8	997.1
Balance at Dec. 31, 2019	449.5		694.0	(250.6)	4.9	897.8
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income			21.4		0.1	21.5
Other comprehensive income (loss)				(3.4)	(0.3)	(3.7)
Stock issued	9.4					9.4
Stock purchased	(4.2)				(0.1)	(4.3)
Advance payments		1.1				1.1
Dividends declared			(6.9)			(6.9)
Balance at Mar. 31, 2020	454.7	1.1	708.5	(254.0)	4.6	914.9
Balance at Dec. 31, 2019	449.5		694.0	(250.6)	4.9	897.8
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income						93.2
Other comprehensive income (loss)						16.9
Balance at Sep. 30, 2020	452.3	1.0	766.5	(233.7)	4.3	990.4
Balance at Mar. 31, 2020	454.7	1.1	708.5	(254.0)	4.6	914.9
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income			37.1			37.1
Other comprehensive income (loss)				9.6	0.2	9.8
Stock issued	3.6					3.6
Stock purchased	(4.6)				(0.6)	(5.2)
Advance payments		(0.6)				(0.6)
Dividends declared			(6.8)			(6.8)
Balance at Jun. 30, 2020	453.7	0.5	738.8	(244.4)	4.2	952.8
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income			34.5		0.1	34.6
Other comprehensive income (loss)				10.7	0.1	10.8
Stock issued	3.1					3.1
Stock purchased	(4.5)				(0.1)	(4.6)
Advance payments		0.5				0.5
Dividends declared			(6.8)			(6.8)
Balance at Sep. 30, 2020	$ 452.3	$ 1.0	$ 766.5	$ (233.7)	$ 4.3	$ 990.4