Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive (loss) income
Balance at beginning of period at Dec. 31, 2018		$ 2.9	$ 3.0	$ 2,341.6	$ (44.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock options exercised			18.1
Purchases of common stock			0.0
Stock-based compensation			1.6
Net earnings	$ 194.1			194.1
Dividends paid in cash				(123.0)
Other comprehensive (loss) income					3.7
Balance at end of period at Mar. 31, 2019	$ 2,397.2	2.9	22.7	2,412.7	(41.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 0.215
Balance at beginning of period at Dec. 31, 2018		2.9	3.0	2,341.6	(44.8)
Balance at end of period at Dec. 31, 2019	$ 2,665.6	2.9	67.2	2,633.9	(38.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 0.870
Stock options exercised			7.4
Purchases of common stock			(52.0)
Stock-based compensation			1.6
Net earnings	$ 202.6			202.6
Dividends paid in cash				(143.6)
Other comprehensive (loss) income					(25.0)
Balance at end of period at Mar. 31, 2020	$ 2,656.6	$ 2.9	$ 24.2	$ 2,692.9	$ (63.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 0.250