Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Net parent investment	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income (loss)	Treasury stock	Noncontrolling interests	ASU 2018-02 Retained earnings	ASU 2018-02 Accumulated other comprehensive income (loss)
Beginning balance, value at Dec. 31, 2014	$ 416.6	$ 0.0	$ 421.3	$ 0.0	$ 0.0	$ (7.3)	$ 0.0	$ 2.6
Beginning balance, shares at Dec. 31, 2014		0
Increase (Decrease) in Stockholders' Equity
Net income (loss)	84.3		79.7					4.6
Other comprehensive income (loss) before reclassifications	(9.2)					(9.2)
Noncontrolling interest distributions	(3.4)							(3.4)
Transactions with parent	29.1		29.1
Ending balance, value at Dec. 31, 2015	517.4	$ 0.0	530.1	0.0	0.0	(16.5)	0.0	3.8
Ending balance, shares at Dec. 31, 2015		0
Increase (Decrease) in Stockholders' Equity
Net income (loss)	44.4		19.2		16.0			9.2
Other comprehensive income (loss) before reclassifications	(2.5)					(2.5)
Noncontrolling interest distributions	(5.4)							(5.4)
Transactions with parent	24.8		24.8
Reclassifications from net parent investment to additional paid in capital	0.0		(125.6)	125.6
Issuance of common stock at separation, value	0.0	$ 0.4		(0.4)
Issuance of common stock at separation, shares		42,101,600
Common stock issued - compensation plans	0.0
Common stock issued - compensation plans, shares		14,800
Tax payments related to vested restricted stock units	(0.3)						(0.3)
Cash distributed to WestRock at Separation	(448.5)		(448.5)
Share-based compensation plans	4.7			4.7
Ending balance, value at Dec. 31, 2016	$ 134.6	$ 0.4	0.0	129.9	16.0	(19.0)	(0.3)	7.6
Ending balance, shares at Dec. 31, 2016	42,115,824	42,116,400
Increase (Decrease) in Stockholders' Equity
Net income (loss)	$ 145.2				126.5			18.7
Other comprehensive income (loss) before reclassifications	7.6					7.6
Noncontrolling interest distributions	(12.3)							(12.3)
Common stock issued - compensation plans	0.0
Common stock issued - compensation plans, shares		85,900
Tax payments related to vested restricted stock units	(1.2)						(1.2)
Exercise of stock options, value	$ 0.2			0.2
Exercise of stock options, shares	7,000	6,600
Share repurchase program	$ (6.6)						(6.6)
Share-based compensation plans	10.4			10.0			0.4
Reclassification of certain deferred tax effects									$ 0.3	$ (0.3)
Ending balance, value at Dec. 31, 2017	$ 277.9	$ 0.4	$ 0.0	$ 140.1	$ 142.8	$ (11.7)	$ (7.7)	$ 14.0
Ending balance, shares at Dec. 31, 2017	42,089,103	42,208,900