Summary of Significant Accounting Policies - Additional Information 2 (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Operations And Summary Of Significant Accounting Policies [Line Items]
Derivative financial instruments, liability		$ 6,000,000
Derivative financial instruments, asset	$ 1,300,000
Fixed Rate Debt
Operations And Summary Of Significant Accounting Policies [Line Items]
Long-term debt, including current portion, Carrying Value	1,100,000,000	1,100,000,000
Level 2 | Fixed Rate Debt
Operations And Summary Of Significant Accounting Policies [Line Items]
Long-term debt, including current portion, Fair Value	1,200,000,000	$ 1,100,000,000
Fair Value, Measurements, Recurring | Level 3
Operations And Summary Of Significant Accounting Policies [Line Items]
Financial assets	0
Financial liabilities	$ 0