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)
Balance at end of period at Mar. 31, 2019		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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock options exercised			40.1
Purchases of common stock			0.0
Stock-based compensation			2.9
Net earnings	$ 398.7			398.7
Dividends paid in cash				(246.1)
Other comprehensive (loss) income					5.4
Balance at end of period at Jun. 30, 2019	$ 2,503.7	2.9	46.0	2,494.2	(39.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cash dividends paid per share of common stock (in dollars per share)	$ 0.430
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
Balance at beginning of period at Mar. 31, 2019		2.9	22.7	2,412.7	(41.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock options exercised			22.0
Purchases of common stock			0.0
Stock-based compensation			1.3
Net earnings	$ 204.6			204.6
Dividends paid in cash				(123.1)
Other comprehensive (loss) income					1.7
Balance at end of period at Jun. 30, 2019	$ 2,503.7	2.9	46.0	2,494.2	(39.4)
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, 2019	$ 2,665.6	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)	$ 0.250
Balance at beginning 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]
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)	$ 0.500
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)	$ 0.250