Supplemental Guarantor Information - Condensed Consolidating Statements of Cash Flows (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Supplemental Guarantor Information [Line Items]
Net cash provided by operating activities	$ 332.3	$ 376.2
Cash flows used in investing activities:
Capital expenditures	(33.6)	(36.8)
Net cash used in investing activities	(33.6)	(36.8)
Cash flows used in financing activities:
Proceeds from borrowings under revolving credit facilities	488.1	67.7
Repayments of borrowings under revolving credit facilities	(474.4)	(13.7)
Repayments of long-term debt	(7.5)	(7.5)
Proceeds from issuance of long-term debt	0.0	2,083.0
Payments to extinguish long-term debt	0.0	(2,121.3)
Payments of debt financing costs	(1.0)	(9.6)
Net change in accounts payable-inventory financing	(110.4)	(85.1)
Premium payments on interest rate cap agreements	(12.6)	0.0
Proceeds from stock option exercises	19.9	7.4
Proceeds from Coworker Stock Purchase Plan	5.4	4.7
Repurchases of common stock	(176.4)	(359.4)
Payment of incentive compensation plan withholding taxes	(8.7)	(42.0)
Dividends	(63.8)	(50.3)
Repayment of intercompany loan	0.0	0.0
Other	3.2	(0.6)
Distributions and advances from (to) affiliates	0.0	0.0
Net cash used in financing activities	(338.2)	(526.7)
Effect of exchange rate changes on cash and cash equivalents	(4.0)	2.6
Net decrease in cash and cash equivalents	(43.5)	(184.7)
Cash and cash equivalents—beginning of period	144.2	263.7	$ 263.7
Cash and cash equivalents—end of period	100.7	79.0	144.2
Consolidating Adjustments
Supplemental Guarantor Information [Line Items]
Net cash provided by operating activities	(14.0)	(33.9)
Cash flows used in investing activities:
Capital expenditures	0.0	0.0
Net cash used in investing activities	0.0	0.0
Cash flows used in financing activities:
Proceeds from borrowings under revolving credit facilities	0.0	0.0
Repayments of borrowings under revolving credit facilities	0.0	0.0
Repayments of long-term debt	0.0	0.0
Proceeds from issuance of long-term debt		0.0
Payments to extinguish long-term debt		0.0
Payments of debt financing costs	0.0	0.0
Net change in accounts payable-inventory financing	0.0	0.0
Premium payments on interest rate cap agreements	0.0
Proceeds from stock option exercises	0.0	0.0
Proceeds from Coworker Stock Purchase Plan	0.0	0.0
Repurchases of common stock	0.0	0.0
Payment of incentive compensation plan withholding taxes	0.0	0.0
Dividends	0.0	0.0
Repayment of intercompany loan	0.0	0.0
Other	0.0	0.0
Distributions and advances from (to) affiliates	(6.7)	7.4
Net cash used in financing activities	(6.7)	7.4
Effect of exchange rate changes on cash and cash equivalents	0.0	0.0
Net decrease in cash and cash equivalents	(20.7)	(26.5)
Cash and cash equivalents—beginning of period	(1.9)	0.0	0.0
Cash and cash equivalents—end of period	(22.6)	(26.5)	(1.9)
Parent Guarantor | Reportable Legal Entities
Supplemental Guarantor Information [Line Items]
Net cash provided by operating activities	0.0	0.0
Cash flows used in investing activities:
Capital expenditures	0.0	0.0
Net cash used in investing activities	0.0	0.0
Cash flows used in financing activities:
Proceeds from borrowings under revolving credit facilities	0.0	0.0
Repayments of borrowings under revolving credit facilities	0.0	0.0
Repayments of long-term debt	0.0	0.0
Proceeds from issuance of long-term debt		0.0
Payments to extinguish long-term debt		0.0
Payments of debt financing costs	0.0	0.0
Net change in accounts payable-inventory financing	0.0	0.0
Premium payments on interest rate cap agreements	0.0
Proceeds from stock option exercises	0.0	0.0
Proceeds from Coworker Stock Purchase Plan	0.0	0.0
Repurchases of common stock	(176.4)	(359.4)
Payment of incentive compensation plan withholding taxes	(8.7)	0.0
Dividends	(63.8)	(50.3)
Repayment of intercompany loan	0.0	0.0
Other	0.0	0.0
Distributions and advances from (to) affiliates	248.9	409.7
Net cash used in financing activities	0.0	0.0
Effect of exchange rate changes on cash and cash equivalents	0.0	0.0
Net decrease in cash and cash equivalents	0.0	0.0
Cash and cash equivalents—beginning of period	0.0	0.0	0.0
Cash and cash equivalents—end of period	0.0	0.0	0.0
Subsidiary Issuer | Reportable Legal Entities
Supplemental Guarantor Information [Line Items]
Net cash provided by operating activities	(71.8)	(22.1)
Cash flows used in investing activities:
Capital expenditures	(24.2)	(26.6)
Net cash used in investing activities	(24.2)	(26.6)
Cash flows used in financing activities:
Proceeds from borrowings under revolving credit facilities	467.5	54.0
Repayments of borrowings under revolving credit facilities	(467.5)	0.0
Repayments of long-term debt	(7.5)	(7.5)
Proceeds from issuance of long-term debt		2,083.0
Payments to extinguish long-term debt		(2,121.3)
Payments of debt financing costs	(1.0)	(9.6)
Net change in accounts payable-inventory financing	(0.9)	(1.2)
Premium payments on interest rate cap agreements	(12.6)
Proceeds from stock option exercises	19.9	7.4
Proceeds from Coworker Stock Purchase Plan	5.4	4.7
Repurchases of common stock	0.0	0.0
Payment of incentive compensation plan withholding taxes	0.0	(16.0)
Dividends	0.0	0.0
Repayment of intercompany loan	0.0	0.0
Other	3.6	0.0
Distributions and advances from (to) affiliates	46.3	(100.5)
Net cash used in financing activities	53.2	(107.0)
Effect of exchange rate changes on cash and cash equivalents	0.0	0.0
Net decrease in cash and cash equivalents	(42.8)	(155.7)
Cash and cash equivalents—beginning of period	113.7	222.7	222.7
Cash and cash equivalents—end of period	70.9	67.0	113.7
Guarantor Subsidiaries
Cash flows used in financing activities:
Payments of debt financing costs		0.0
Guarantor Subsidiaries | Reportable Legal Entities
Supplemental Guarantor Information [Line Items]
Net cash provided by operating activities	343.9	391.5
Cash flows used in investing activities:
Capital expenditures	(1.9)	(4.3)
Net cash used in investing activities	(1.9)	(4.3)
Cash flows used in financing activities:
Proceeds from borrowings under revolving credit facilities	0.0	0.0
Repayments of borrowings under revolving credit facilities	0.0	0.0
Repayments of long-term debt	0.0	0.0
Proceeds from issuance of long-term debt		0.0
Payments to extinguish long-term debt		0.0
Payments of debt financing costs	0.0
Net change in accounts payable-inventory financing	(100.8)	(83.9)
Premium payments on interest rate cap agreements	0.0
Proceeds from stock option exercises	0.0	0.0
Proceeds from Coworker Stock Purchase Plan	0.0	0.0
Repurchases of common stock	0.0	0.0
Payment of incentive compensation plan withholding taxes	0.0	(24.0)
Dividends	0.0	0.0
Repayment of intercompany loan	47.5	34.3
Other	(0.2)	(0.1)
Distributions and advances from (to) affiliates	(288.5)	(316.6)
Net cash used in financing activities	(342.0)	(390.3)
Effect of exchange rate changes on cash and cash equivalents	0.0	0.0
Net decrease in cash and cash equivalents	0.0	(3.1)
Cash and cash equivalents—beginning of period	0.0	3.1	3.1
Cash and cash equivalents—end of period	0.0	0.0	0.0
Non-Guarantor Subsidiaries | Reportable Legal Entities
Supplemental Guarantor Information [Line Items]
Net cash provided by operating activities	74.2	40.7
Cash flows used in investing activities:
Capital expenditures	(7.5)	(5.9)
Net cash used in investing activities	(7.5)	(5.9)
Cash flows used in financing activities:
Proceeds from borrowings under revolving credit facilities	20.6	13.7
Repayments of borrowings under revolving credit facilities	(6.9)	(13.7)
Repayments of long-term debt	0.0	0.0
Proceeds from issuance of long-term debt		0.0
Payments to extinguish long-term debt		0.0
Payments of debt financing costs	0.0	0.0
Net change in accounts payable-inventory financing	(8.7)	0.0
Premium payments on interest rate cap agreements	0.0
Proceeds from stock option exercises	0.0	0.0
Proceeds from Coworker Stock Purchase Plan	0.0	0.0
Repurchases of common stock	0.0	0.0
Payment of incentive compensation plan withholding taxes	0.0	(2.0)
Dividends	0.0	0.0
Repayment of intercompany loan	(47.5)	(34.3)
Other	(0.2)	(0.5)
Distributions and advances from (to) affiliates	0.0	0.0
Net cash used in financing activities	(42.7)	(36.8)
Effect of exchange rate changes on cash and cash equivalents	(4.0)	2.6
Net decrease in cash and cash equivalents	20.0	0.6
Cash and cash equivalents—beginning of period	32.4	37.9	37.9
Cash and cash equivalents—end of period	52.4	38.5	32.4
Co-Issuer | Reportable Legal Entities
Supplemental Guarantor Information [Line Items]
Net cash provided by operating activities	0.0	0.0
Cash flows used in investing activities:
Capital expenditures	0.0	0.0
Net cash used in investing activities	0.0	0.0
Cash flows used in financing activities:
Proceeds from borrowings under revolving credit facilities	0.0	0.0
Repayments of borrowings under revolving credit facilities	0.0	0.0
Repayments of long-term debt	0.0	0.0
Proceeds from issuance of long-term debt		0.0
Payments to extinguish long-term debt		0.0
Payments of debt financing costs	0.0	0.0
Net change in accounts payable-inventory financing	0.0	0.0
Premium payments on interest rate cap agreements	0.0
Proceeds from stock option exercises	0.0	0.0
Proceeds from Coworker Stock Purchase Plan	0.0	0.0
Repurchases of common stock	0.0	0.0
Payment of incentive compensation plan withholding taxes	0.0	0.0
Dividends	0.0	0.0
Repayment of intercompany loan	0.0	0.0
Other	0.0	0.0
Distributions and advances from (to) affiliates	0.0	0.0
Net cash used in financing activities	0.0	0.0
Effect of exchange rate changes on cash and cash equivalents	0.0	0.0
Net decrease in cash and cash equivalents	0.0	0.0
Cash and cash equivalents—beginning of period	0.0	0.0	0.0
Cash and cash equivalents—end of period	$ 0.0	$ 0.0	$ 0.0