Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Treasury Stock	AOCI Attributable to Parent
Balance at Dec. 31, 2019	$ 364.9	$ 0.6	$ 555.7	$ 1,008.2	$ (823.5)	$ (376.1)
Balance at Dec. 31, 2019		47,992,348
Balance at Dec. 31, 2019					14,271,047
Stock issuance, net, shares		249,573
Cash dividends - per common share	(29.2)			(29.2)
Share-based employee compensation	(3.1)		(3.1)
Net earnings (loss)	(121.9)			(121.9)
Other comprehensive income (Loss)	266.3					266.3
Acquisition of treasury stock	(34.4)				$ (34.4)
Acquisition of treasury stock, shares		382,170			(382,170)
Balance at Sep. 30, 2020	442.6	$ 0.6	552.6	857.1	$ (857.9)	(109.8)
Balance at Sep. 30, 2020		47,859,751
Balance at Sep. 30, 2020					14,653,217
Balance at Jun. 30, 2020	402.9	$ 0.6	551.7	812.8	$ (857.9)	(104.3)
Balance at Jun. 30, 2020		47,856,179
Balance at Jun. 30, 2020					14,653,217
Stock issuance, net, shares		3,572
Cash dividends - per common share	(9.7)			(9.7)
Share-based employee compensation	0.9		0.9
Net earnings (loss)	54.0			54.0
Other comprehensive income (Loss)	(5.5)					(5.5)
Balance at Sep. 30, 2020	442.6	$ 0.6	552.6	857.1	$ (857.9)	(109.8)
Balance at Sep. 30, 2020		47,859,751
Balance at Sep. 30, 2020					14,653,217
Balance at Dec. 31, 2020	$ 450.9	$ 0.6	553.7	869.8	$ (863.9)	(109.3)
Balance at Dec. 31, 2020	47,913,821	47,913,821
Balance at Dec. 31, 2020					14,685,510
Stock issuance, net, shares		140,823
Cash dividends - per common share	$ (30.5)			(30.5)
Share-based employee compensation	4.0		4.0
Net earnings (loss)	141.3			141.3
Other comprehensive income (Loss)	6.5					6.5
Acquisition of treasury stock	(50.0)				$ (50.0)
Acquisition of treasury stock, shares		507,022			(507,022)
Balance at Sep. 30, 2021	$ 522.2	$ 0.6	557.7	980.6	$ (913.9)	(102.8)
Balance at Sep. 30, 2021	47,547,622	47,547,622
Balance at Sep. 30, 2021					15,192,532
Balance at Jun. 30, 2021	$ 498.3	$ 0.6	554.7	939.8	$ (893.9)	(102.9)
Balance at Jun. 30, 2021		47,732,943
Balance at Jun. 30, 2021					15,005,603
Stock issuance, net, shares		1,608
Cash dividends - per common share	(10.0)			(10.0)
Share-based employee compensation	3.0		3.0
Net earnings (loss)	50.8			50.8
Other comprehensive income (Loss)	0.1					0.1
Acquisition of treasury stock	(20.0)				$ (20.0)
Acquisition of treasury stock, shares		186,929			(186,929)
Balance at Sep. 30, 2021	$ 522.2	$ 0.6	$ 557.7	$ 980.6	$ (913.9)	$ (102.8)
Balance at Sep. 30, 2021	47,547,622	47,547,622
Balance at Sep. 30, 2021					15,192,532