Income Taxes - Schedule of Changes in Balance of Gross Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Contingency [Line Items]
Beginning balance	$ 34,876
Decrease—Lapse of statute of limitations	(4,309)
Accrued in connection with the ETFS Acquisition		$ 38,488
Increases	416	346
Foreign currency translation	1,118	(3,958)
Ending balance	32,101	34,876
Unrecognized Tax Benefits [Member]
Income Tax Contingency [Line Items]
Beginning balance	28,101
Decrease—Lapse of statute of limitations	(2,999)
Accrued in connection with the ETFS Acquisition		31,317
Increases	0
Foreign currency translation	896	(3,216)
Ending balance	25,998	28,101
Interest And Penalties [Member]
Income Tax Contingency [Line Items]
Beginning balance	6,775
Decrease—Lapse of statute of limitations	(1,310)
Accrued in connection with the ETFS Acquisition		7,171
Increases	416	346
Foreign currency translation	222	(742)
Ending balance	$ 6,103	$ 6,775