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, 2017	$ 384.1	$ 0.6	$ 516.8	$ 598.2	$ (385.6)	$ (345.9)
Balance at Dec. 31, 2017		52,772,139
Balance at Dec. 31, 2017					8,010,597
Cumulative effect impact of ASU adoption | ASU 2018-02 [Member]	(54.3)			54.3		(54.3)
Stock issuance, net		751,279
Share-based employee compensation	25.4		25.4
Net earnings	151.3			151.3
Other comprehensive (loss) income	(9.0)					(9.0)
Deferred accelerated stock repurchase	(30.0)		(30.0)
Acquisition of treasury stock	(226.1)				$ (226.1)
Acquisition of treasury stock, shares		(3,567,733)			3,567,733
Balance at Sep. 30, 2018	295.7	$ 0.6	512.2	803.8	$ (611.7)	(409.2)
Balance at Sep. 30, 2018		49,955,685
Balance at Sep. 30, 2018					11,578,330
Balance at Jun. 30, 2018	368.9	$ 0.6	535.7	727.6	$ (490.6)	(404.4)
Balance at Jun. 30, 2018		51,638,049
Balance at Jun. 30, 2018					9,796,413
Stock issuance, net		99,553
Share-based employee compensation	6.5		6.5
Net earnings	76.2			76.2
Other comprehensive (loss) income	(4.8)					(4.8)
Deferred accelerated stock repurchase	(30.0)		(30.0)
Acquisition of treasury stock	(121.1)				$ (121.1)
Acquisition of treasury stock, shares		(1,781,917)			1,781,917
Balance at Sep. 30, 2018	295.7	$ 0.6	512.2	803.8	$ (611.7)	(409.2)
Balance at Sep. 30, 2018		49,955,685
Balance at Sep. 30, 2018					11,578,330
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	48,808,239
Balance at Dec. 31, 2018					12,745,485
Cumulative effect impact of ASU adoption | ASU 2017-12 [Member]	$ 0.1			(0.1)		0.1
Stock issuance, net		617,984
Cash dividends - $0.175 per common share	(26.2)			(26.2)
Share-based employee compensation	2.0		2.0
Net earnings	166.8			166.8
Other comprehensive (loss) income	79.9					79.9
Acquisition of treasury stock	(81.2)				$ (81.2)
Acquisition of treasury stock, shares		(994,995)			994,995
Balance at Sep. 30, 2019	$ 367.3	$ 0.6	549.4	970.3	$ (773.4)	(379.6)
Balance at Sep. 30, 2019	48,431,228	48,431,228
Balance at Sep. 30, 2019					13,740,480
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
Stock issuance, net		116,586
Cash dividends - $0.175 per common share	(8.6)			(8.6)
Share-based employee compensation	11.3		11.3
Net earnings	73.2			73.2
Other comprehensive (loss) income	81.4					81.4
Acquisition of treasury stock	(33.1)				$ (33.1)
Acquisition of treasury stock, shares		(347,304)			347,304
Balance at Sep. 30, 2019	$ 367.3	$ 0.6	$ 549.4	$ 970.3	$ (773.4)	$ (379.6)
Balance at Sep. 30, 2019	48,431,228	48,431,228
Balance at Sep. 30, 2019					13,740,480