Basis of Presentation and Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 190.8	$ 370.6
Restricted cash - current	$ 32.9	$ 32.9
Restricted Cash, Current, Asset, Statement of Financial Position [Extensible List]	us-gaap:PrepaidExpenseAndOtherAssetsCurrent	us-gaap:PrepaidExpenseAndOtherAssetsCurrent
Restricted cash - noncurrent	$ 0.1	$ 0.1
Restricted Cash, Noncurrent, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Total cash, cash equivalents and restricted cash	$ 223.8	$ 403.6	$ 301.5	$ 335.9