Income Taxes - Korean and Singapore subsidiary commitments (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax [Line Items]
Undistributed Earnings of Foreign Subsidiaries	$ 66.6
Korea Tax Authority [Member]
Income Tax [Line Items]
Income tax benefit estimate attributable to the tax status of subsidiary			$ 4.0
Income tax expense benefit per diluted share			$ 0.03
Inland Revenue, Singapore (IRAS) [Member]
Income Tax [Line Items]
Income tax benefit estimate attributable to the tax status of subsidiary	$ 9.4	$ 5.8	$ 6.3
Income tax expense benefit per diluted share	$ 0.07	$ 0.04	$ 0.04
additional effective tax rate benefit	$ 5.4	$ 3.3	$ 3.6