Concentration of Credit Risk - Additional Information (Detail) - Credit Concentration Risk [Member] $ in Millions	Dec. 31, 2020 USD ($)
Corporate Bonds [Member]
Concentration Risk [Line Items]
Fair value of financial instruments	$ 144.8
Money Market Funds [Member]
Concentration Risk [Line Items]
Fair value of financial instruments	82.1
Mortgage Backed Securities [Member]
Concentration Risk [Line Items]
Fair value of financial instruments	55.5
U.S. Government Agency Securities [Member]
Concentration Risk [Line Items]
Fair value of financial instruments	40.4
Asset Backed Securities [Member]
Concentration Risk [Line Items]
Fair value of financial instruments	37.1
Mutual Funds [Member]
Concentration Risk [Line Items]
Fair value of financial instruments	5.0
Supranational Bonds [Member]
Concentration Risk [Line Items]
Fair value of financial instruments	4.8
U.S. Treasuries [Member]
Concentration Risk [Line Items]
Fair value of financial instruments	$ 4.5