Commitments and Contingencies - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Contingencies And Commitments [Line Items]
Deductible for marine liability coverage including personal injury claims, per first occurrence	$ 5,000,000
Range of deductible for liability coverage for personal injury claims, lower limit	5,000,000
Range of deductible for liability coverage for personal injury claims, upper limit	100,000,000
Total Contingent Liabilities Under Letters of Credit and Bonds [Member]
Contingencies And Commitments [Line Items]
Contingent liability under letters of credit and other bonds	25,700,000
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	17,100,000
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
Range of deductible for liability coverage for personal injury claims, lower limit	25,000,000
Range of deductible for liability coverage for personal injury claims, upper limit	100,000,000
Personal Injury Claims [Member]
Contingencies And Commitments [Line Items]
Personal injury claims recorded	25,800,000	$ 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	$ 20,900,000	$ 22,700,000