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Stockholders' Equity - (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	1,300,000		1,300,000
Stock-based compensation expense	$ 2.5	$ 0.9	$ 7.3	$ 3.0
Share-based Payment Arrangement, Expense, Tax Benefit	0.6	0.2	1.9	0.8
Payment, Tax Withholding, Share-based Payment Arrangement	0.0	$ 0.0	0.7	$ 0.4
Equity Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount	$ 12.7		$ 12.7
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based awards granted			377,822
Grant-date fair value of awards per share			$ 23.46
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based awards granted			120,382
Grant-date fair value of awards per share			$ 27.67