CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Millions	Common Stock	Common Stock and Additional Paid in Capital	Retained Earnings	Accumulated Other Comprehensive (Loss) Income	Non-controlling Interests	Total
Balance at Dec. 31, 2018		$ 136.4	$ 4,637.9	$ (102.7)	$ 7.9	$ 4,679.5
Balance (in shares) at Dec. 31, 2018	66,882,000
Increase (Decrease) in Stockholders' Equity
Net income			190.1		1.5	191.6
Other comprehensive income (loss)				6.8		6.8
Stock-based compensation, net		(1.3)				(1.3)
Stock-based compensation, net (in shares)	333,000
Stock options exercised		0.8				0.8
Stock options exercised (in shares)	20,000
Cash dividends - $0.55 and $0.625 per share for the quarter ended March 31, 2019 and March 31, 2020, respectively, and $0.55 and $0.625 per share for the quarter ended June 30, 2019 and June 30, 2020, respectively			(38.2)			(38.2)
Balance at Mar. 31, 2019		135.9	4,789.8	(95.9)	9.4	4,839.2
Balance (in shares) at Mar. 31, 2019	67,235,000
Balance at Dec. 31, 2018		136.4	4,637.9	(102.7)	7.9	4,679.5
Balance (in shares) at Dec. 31, 2018	66,882,000
Increase (Decrease) in Stockholders' Equity
Net income						375.9
Other comprehensive income (loss)						8.0
Repurchase of common shares						$ (50.0)
Repurchase of common shares (in shares)						600,000
Balance at Jun. 30, 2019		99.7	4,936.0	(94.7)	8.5	$ 4,949.5
Balance (in shares) at Jun. 30, 2019	66,654,000
Balance at Mar. 31, 2019		135.9	4,789.8	(95.9)	9.4	4,839.2
Balance (in shares) at Mar. 31, 2019	67,235,000
Increase (Decrease) in Stockholders' Equity
Net income			183.1		1.2	184.3
Other comprehensive income (loss)				1.2		1.2
Noncontrolling interest purchased					(0.4)	(0.4)
Dividend to noncontrolling interest holder					(1.7)	(1.7)
Stock-based compensation, net		13.8				13.8
Stock-based compensation, net (in shares)	12,000
Repurchase of common shares		(50.0)				(50.0)
Repurchase of common shares (in shares)	(593,000)
Cash dividends - $0.55 and $0.625 per share for the quarter ended March 31, 2019 and March 31, 2020, respectively, and $0.55 and $0.625 per share for the quarter ended June 30, 2019 and June 30, 2020, respectively			(36.9)			(36.9)
Balance at Jun. 30, 2019		99.7	4,936.0	(94.7)	8.5	4,949.5
Balance (in shares) at Jun. 30, 2019	66,654,000
Balance at Dec. 31, 2019		122.2	5,189.5	(105.1)	7.5	$ 5,214.1
Balance (in shares) at Dec. 31, 2019	66,854,000					66,854,000
Increase (Decrease) in Stockholders' Equity
Net income			61.7		1.2	$ 62.9
Other comprehensive income (loss)				(31.4)		(31.4)
Noncontrolling interest purchased		(6.9)			(1.1)	(8.0)
Dividend to noncontrolling interest holder					(0.5)	(0.5)
Stock-based compensation, net		3.8				3.8
Stock-based compensation, net (in shares)	111,000
Stock options exercised		0.3				0.3
Stock options exercised (in shares)	6,000
Repurchase of common shares		(119.3)	(180.7)			(300.0)
Repurchase of common shares (in shares)	(3,330,000)
Cash dividends - $0.55 and $0.625 per share for the quarter ended March 31, 2019 and March 31, 2020, respectively, and $0.55 and $0.625 per share for the quarter ended June 30, 2019 and June 30, 2020, respectively			(41.9)			(41.9)
Balance at Mar. 31, 2020		0.1	5,028.6	(136.5)	7.1	4,899.3
Balance (in shares) at Mar. 31, 2020	63,641,000
Balance at Dec. 31, 2019		122.2	5,189.5	(105.1)	7.5	$ 5,214.1
Balance (in shares) at Dec. 31, 2019	66,854,000					66,854,000
Increase (Decrease) in Stockholders' Equity
Net income						$ 143.6
Other comprehensive income (loss)						(19.0)
Repurchase of common shares						$ (300.0)
Repurchase of common shares (in shares)						3,300,000
Balance at Jun. 30, 2020		9.1	5,068.9	(124.1)	7.6	$ 4,961.5
Balance (in shares) at Jun. 30, 2020	63,654,000					63,654,000
Balance at Mar. 31, 2020		0.1	5,028.6	(136.5)	7.1	$ 4,899.3
Balance (in shares) at Mar. 31, 2020	63,641,000
Increase (Decrease) in Stockholders' Equity
Net income			80.2		0.5	80.7
Other comprehensive income (loss)				12.4		12.4
Stock-based compensation, net		9.0				$ 9.0
Stock-based compensation, net (in shares)	13,000
Repurchase of common shares (in shares)						0
Cash dividends - $0.55 and $0.625 per share for the quarter ended March 31, 2019 and March 31, 2020, respectively, and $0.55 and $0.625 per share for the quarter ended June 30, 2019 and June 30, 2020, respectively			(39.9)			$ (39.9)
Balance at Jun. 30, 2020		$ 9.1	$ 5,068.9	$ (124.1)	$ 7.6	$ 4,961.5
Balance (in shares) at Jun. 30, 2020	63,654,000					63,654,000