Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Par	Additional Paid-In Capital	Accumulated Retained Earnings	Other Comprehensive Income (Loss)	Treasury Stock
Balance at Dec. 31, 2017	$ 1,495.1	$ 1.1	$ 774.3	$ 1,496.1	$ (45.0)	$ (731.4)
Increase (Decrease) in Stockholders' Equity
Net income	61.6			61.6
Dividends paid on common stock	(11.2)			(11.2)
Impact of new accounting pronouncements	3.8			2.2	1.6
Change in other comprehensive income – net of tax	35.6				35.6
Stock based compensation	7.7		13.4			(5.7)
Acquisition of treasury stock	(30.1)					(30.1)
Balance at Mar. 31, 2018	1,562.5	1.1	787.7	1,548.7	(7.8)	(767.2)
Balance at Dec. 31, 2017	1,495.1	1.1	774.3	1,496.1	(45.0)	(731.4)
Increase (Decrease) in Stockholders' Equity
Net income	130.4
Change in other comprehensive income – net of tax	(37.4)
Balance at Jun. 30, 2018	1,399.8	1.1	792.0	1,606.2	(80.8)	(918.7)
Balance at Mar. 31, 2018	1,562.5	1.1	787.7	1,548.7	(7.8)	(767.2)
Increase (Decrease) in Stockholders' Equity
Net income	68.8			68.8
Dividends paid on common stock	(11.3)			(11.3)
Change in other comprehensive income – net of tax	(73.0)				(73.0)
Stock based compensation	3.7		4.3			(0.6)
Acquisition of treasury stock	(150.9)					(150.9)
Balance at Jun. 30, 2018	1,399.8	1.1	792.0	1,606.2	(80.8)	(918.7)
Balance at Dec. 31, 2018	1,322.0	1.1	798.3	1,726.5	(108.0)	(1,095.9)
Increase (Decrease) in Stockholders' Equity
Net income	72.2			72.2
Dividends paid on common stock	(12.7)			(12.7)
Change in other comprehensive income – net of tax	(5.9)				(5.9)
Stock based compensation	8.0		13.5			(5.5)
Acquisition of treasury stock	(11.2)					(11.2)
Balance at Mar. 31, 2019	1,372.4	1.1	811.8	1,786.0	(113.9)	(1,112.6)
Balance at Dec. 31, 2018	1,322.0	1.1	798.3	1,726.5	(108.0)	(1,095.9)
Increase (Decrease) in Stockholders' Equity
Net income	153.1
Change in other comprehensive income – net of tax	(10.1)
Balance at Jun. 30, 2019	1,442.4	1.1	817.9	1,854.1	(118.1)	(1,112.6)
Balance at Mar. 31, 2019	1,372.4	1.1	811.8	1,786.0	(113.9)	(1,112.6)
Increase (Decrease) in Stockholders' Equity
Net income	80.9			80.9
Dividends paid on common stock	(12.8)			(12.8)
Change in other comprehensive income – net of tax	(4.2)				(4.2)
Stock based compensation	6.1		6.1
Balance at Jun. 30, 2019	$ 1,442.4	$ 1.1	$ 817.9	$ 1,854.1	$ (118.1)	$ (1,112.6)