Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Retained Earnings	Treasury Stock	Non-Controlling Interest in Subsidiaries	Commodity contracts	Commodity contracts Accumulated Other Comprehensive Income	Cumulative Effect, Period of Adoption, Adjustment [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Retained Earnings
Beginning balance (shares) at Dec. 31, 2018		90,478,075				(12,477,780)
Beginning balance at Dec. 31, 2018	$ 1,808.1	$ 0.9	$ 1,135.4	$ 28.6	$ 981.8	$ (514.1)	$ 175.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	238.2				226.6		11.6
Other comprehensive income (loss) related to commodity contracts, net								$ (2.7)	$ (2.7)
Common stock dividends	(42.5)				(42.5)		0.0
Distribution to non-controlling interest	(15.6)						(15.6)
Equity-based compensation expense	$ 11.8		11.6				0.2
Repurchase of common stock (shares)	(2,938,722)					(2,938,722)
Repurchase of common stock	$ (104.8)					$ (104.8)	0.0
Taxes due to the net settlement of equity-based compensation	$ (6.9)		(6.9)				0.0
Exercise of equity-based awards (shares)		383,623
Other (shares)	0
Other	$ 0.6		0.2	0.4	0.0	0.0	0.0
Ending balance at Jun. 30, 2019	1,886.2	$ 0.9	1,140.3	26.3	1,165.9	$ (618.9)	171.7
Ending balance (shares) at Jun. 30, 2019		90,861,698				(15,416,502)
Beginning balance (shares) at Mar. 31, 2019		90,722,641				(13,769,424)
Beginning balance at Mar. 31, 2019	1,898.5	$ 0.9	1,135.5	39.3	1,110.1	$ (560.3)	173.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	83.8				77.3		6.5
Other comprehensive income (loss) related to commodity contracts, net								(13.0)	(13.0)
Common stock dividends	(21.5)				(21.5)		0.0
Distribution to non-controlling interest	(7.9)						(7.9)
Equity-based compensation expense	$ 6.8		6.7				0.1
Repurchase of common stock (shares)	(1,647,078)					(1,647,078)
Repurchase of common stock	$ (58.6)					$ (58.6)	0.0
Taxes due to the net settlement of equity-based compensation	$ (2.4)		(2.4)				0.0
Exercise of equity-based awards (shares)		139,057
Other (shares)	0
Other	$ 0.5		0.5	0.0	0.0	0.0	0.0
Ending balance at Jun. 30, 2019	1,886.2	$ 0.9	1,140.3	26.3	1,165.9	$ (618.9)	171.7
Ending balance (shares) at Jun. 30, 2019		90,861,698				(15,416,502)
Beginning balance (shares) at Dec. 31, 2019		90,987,025				(17,516,814)
Beginning balance at Dec. 31, 2019	1,835.3	$ 0.9	1,151.9	0.1	1,205.6	$ (692.2)	169.0			$ (6.5)	$ (6.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(208.5)				(226.7)		18.2
Other comprehensive income (loss) related to commodity contracts, net								0.3	0.3
Common stock dividends	(46.0)				(46.0)		0.0
Distribution to non-controlling interest	(16.8)						(16.8)
Equity-based compensation expense	$ 11.0		10.9				0.1
Repurchase of common stock (shares)	(58,713)					(58,713)
Repurchase of common stock	$ (1.9)						0.0
Repurchase of Non-Controlling Interest	(5.8)		(0.8)				(5.0)
Taxes due to the net settlement of equity-based compensation	$ (1.9)		(1.9)				0.0
Exercise of equity-based awards (shares)	246,463	245,939
Other	$ 0.1		0.0		0.0	$ 0.0	0.0
Ending balance at Jun. 30, 2020	1,559.3	$ 0.9	1,160.1	0.5	926.4	$ (694.1)	165.5
Ending balance (shares) at Jun. 30, 2020		91,232,964				(17,575,527)
Beginning balance (shares) at Mar. 31, 2020		91,089,920				(17,575,527)
Beginning balance at Mar. 31, 2020	1,489.9	$ 0.9	1,157.4	1.2	861.6	$ (694.1)	162.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	98.5				87.7		10.8
Other comprehensive income (loss) related to commodity contracts, net								$ (1.1)	$ (1.1)
Common stock dividends	(22.9)				(22.9)		0.0
Distribution to non-controlling interest	(8.2)						(8.2)
Equity-based compensation expense	$ 4.7		4.7				0.0
Repurchase of common stock (shares)	0
Repurchase of Non-Controlling Interest	$ (0.8)		(0.8)
Taxes due to the net settlement of equity-based compensation	$ (1.2)		(1.2)				0.0
Exercise of equity-based awards (shares)	143,044	143,044
Other (shares)	0
Other	$ 0.4		0.0	0.4	0.0	0.0	0.0
Ending balance at Jun. 30, 2020	$ 1,559.3	$ 0.9	$ 1,160.1	$ 0.5	$ 926.4	$ (694.1)	$ 165.5
Ending balance (shares) at Jun. 30, 2020		91,232,964				(17,575,527)