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, 2019		$ 2.9	$ 67.2	$ 2,633.9	$ (38.4)
Balance at end of period at Mar. 31, 2020		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)	$ 0.25
Balance at beginning of period at Dec. 31, 2019		2.9	67.2	2,633.9	(38.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock options exercised			26.3
Purchases of common stock			(52.0)
Stock-based compensation			2.9
Net earnings	$ 441.5			441.5
Dividends paid in cash				(286.8)
Other comprehensive (loss) income					(14.5)
Balance at end of period at Jun. 30, 2020	$ 2,783.0	2.9	44.4	2,788.6	(52.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 0.50
Balance at beginning of period at Dec. 31, 2019		2.9	67.2	2,633.9	(38.4)
Balance at end of period at Dec. 31, 2020	$ 2,733.2	2.9	61.9	2,689.6	(21.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 1.40
Balance at beginning of period at Mar. 31, 2020		2.9	24.2	2,692.9	(63.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock options exercised			18.9
Purchases of common stock			0.0
Stock-based compensation			1.3
Net earnings	$ 238.9			238.9
Dividends paid in cash				(143.2)
Other comprehensive (loss) income					10.5
Balance at end of period at Jun. 30, 2020	$ 2,783.0	2.9	44.4	2,788.6	(52.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 0.25
Balance at beginning of period at Dec. 31, 2020	$ 2,733.2	2.9	61.9	2,689.6	(21.2)
Balance at end of period at Mar. 31, 2021		2.9	70.0	2,739.4	(25.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 0.28
Balance at beginning of period at Dec. 31, 2020	$ 2,733.2	2.9	61.9	2,689.6	(21.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock options exercised			13.6
Purchases of common stock			0.0
Stock-based compensation			2.9
Net earnings	450.3			450.3
Dividends paid in cash				(321.6)
Other comprehensive (loss) income					2.4
Balance at end of period at Jun. 30, 2021	$ 2,880.8	2.9	78.4	2,818.3	(18.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 0.56
Balance at beginning of period at Mar. 31, 2021		2.9	70.0	2,739.4	(25.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock options exercised			7.0
Purchases of common stock			0.0
Stock-based compensation			1.4
Net earnings	$ 239.7			239.7
Dividends paid in cash				(160.8)
Other comprehensive (loss) income					6.8
Balance at end of period at Jun. 30, 2021	$ 2,880.8	$ 2.9	$ 78.4	$ 2,818.3	$ (18.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 0.28