Other operating income (expense) - Additional Information (Detail) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) InsuranceCarrier	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Component Of Other Income And Expense [Line Items]
Number of insurance carriers for which agreed to reimburse litigation costs | InsuranceCarrier			1
Other income, net			$ 7,444	$ 644	$ 170
Proceeds from sale of business			2,925
Gain from sale of business			$ 3,000
Insurance and Risk Management Business
Component Of Other Income And Expense [Line Items]
Proceeds from sale of business	$ 3,250
Gain from sale of business	$ 3,000
Sale of Excess Property
Component Of Other Income And Expense [Line Items]
Other income, net		$ 4,400