Commitments and Contingencies - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Contingencies And Commitments [Line Items]
Deductible for marine liability coverage including personal injury claims, per first occurrence	$ 5,000,000.0
Range of deductible for liability coverage for personal injury claims, lower limit	5,000,000.0
Range of deductible for liability coverage for personal injury claims, upper limit	100,000,000.0
Total Contingent Liabilities Under Letters of Credit and Bonds [Member]
Contingencies And Commitments [Line Items]
Contingent liability under letters of credit and other bonds	41,700,000
Potentially Collateralized Contingent Liability Under Letters Of Credit and Bonds [Member]
Contingencies And Commitments [Line Items]
Contingent liability under letters of credit and other bonds	33,200,000
Windstorms in U.S. Gulf of Mexico [Member]
Contingencies And Commitments [Line Items]
Deductible for marine liability coverage including personal injury claims, per first occurrence	25,000,000.0
Range of deductible for liability coverage for personal injury claims, lower limit	25,000,000.0
Range of deductible for liability coverage for personal injury claims, upper limit	100,000,000.0
Personal Injury Claims [Member]
Contingencies And Commitments [Line Items]
Personal injury claims recorded	25,200,000	$ 27,900,000
Personal Injury Claims [Member] | Accrued Liabilities [Member]
Contingencies And Commitments [Line Items]
Personal injury claims recorded	4,900,000	5,200,000
Personal Injury Claims [Member] | Other Liabilities [Member]
Contingencies And Commitments [Line Items]
Personal injury claims recorded	$ 20,300,000	$ 22,700,000