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Stockholders' Equity - (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 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	$ 3.4	$ 1.2	$ 4.8	$ 2.1
Share-based Payment Arrangement, Expense, Tax Benefit	0.9	0.3	1.3	0.5
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	$ 12.2		$ 12.2
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based awards granted			371,267
Grant-date fair value of awards per share			$ 23.18
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