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, 2018	$ 226.0	$ 0.6	$ 547.4	$ 829.8	$ (692.2)	$ (459.6)
Balance at Dec. 31, 2018		48,808,239
Balance at Dec. 31, 2018					12,745,485
Stock issuance, net		501,398
Cash dividends - per common share	(17.6)			(17.6)
Share-based employee compensation	(9.3)		(9.3)
Net earnings (loss)	93.6			93.6
Other comprehensive income (loss)	(1.5)					(1.5)
Acquisition of treasury stock	(48.1)				$ (48.1)
Acquisition of treasury stock, shares		(647,691)			647,691
Balance at Jun. 30, 2019	243.1	$ 0.6	538.1	905.7	$ (740.3)	(461.0)
Balance at Jun. 30, 2019		48,661,946
Balance at Jun. 30, 2019					13,393,176
Balance at Mar. 31, 2019	245.1	$ 0.6	553.3	859.9	$ (712.2)	(456.5)
Balance at Mar. 31, 2019		48,640,635
Balance at Mar. 31, 2019					13,077,171
Stock issuance, net		337,316
Cash dividends - per common share	(8.7)			(8.7)
Share-based employee compensation	(15.2)		(15.2)
Net earnings (loss)	54.5			54.5
Other comprehensive income (loss)	(4.5)					(4.5)
Acquisition of treasury stock	(28.1)				$ (28.1)
Acquisition of treasury stock, shares		(316,005)			316,005
Balance at Jun. 30, 2019	243.1	$ 0.6	538.1	905.7	$ (740.3)	(461.0)
Balance at Jun. 30, 2019		48,661,946
Balance at Jun. 30, 2019					13,393,176
Retained earnings | ASU 2017-12 [Member]				(0.1)		0.1
Retained earnings	1,008.2
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	47,992,348
Balance at Dec. 31, 2019					14,271,047
Stock issuance, net		246,001
Cash dividends - per common share	$ (19.5)			(19.5)
Share-based employee compensation	(4.0)		(4.0)
Net earnings (loss)	(175.9)			(175.9)
Other comprehensive income (loss)	271.8					271.8
Acquisition of treasury stock	(34.4)				$ (34.4)
Acquisition of treasury stock, shares		(382,170)			382,170
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	47,856,179
Balance at Jun. 30, 2020					14,653,217
Balance at Mar. 31, 2020	$ 370.4	$ 0.6	557.3	772.1	$ (857.9)	(101.7)
Balance at Mar. 31, 2020		47,659,955
Balance at Mar. 31, 2020					14,653,217
Stock issuance, net		196,224
Cash dividends - per common share	(9.6)			(9.6)
Share-based employee compensation	(5.6)		(5.6)
Net earnings (loss)	50.3			50.3
Other comprehensive income (loss)	(2.6)					(2.6)
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	47,856,179
Balance at Jun. 30, 2020					14,653,217
Retained earnings	$ 812.8