Subsequent Event - Additional Information (Detail) - USD ($)			3 Months Ended
	Apr. 20, 2018	Apr. 17, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
$900.0 Million Revolving Credit Facility
Subsequent Event [Line Items]
Total leverage covenant ratio				5.00%
$900.0 Million Revolving Credit Facility | Revolving Credit Facility
Subsequent Event [Line Items]
Line of credit facility maximum borrowing capacity				$ 900,000,000	$ 900,000,000
Debt maturity period				Jul. 31, 2020
Subsequent Event | Non-Recourse Senior Secured Notes | Private Placement
Subsequent Event [Line Items]
Aggregate principal amount	$ 159,500,000
Stated interest rate	4.43%
Scheduled maturity term	20 years
Expected project completion period	first quarter of 2020
Notes issuance costs	$ 3,500,000
Subsequent Event | New Credit Agreement
Subsequent Event [Line Items]
Line of credit facility maximum borrowing capacity		$ 1,000,000,000
Debt maturity period		Apr. 30, 2023
Total leverage covenant ratio		5.50%
Line of credit facility, increases in the revolving commitments or incremental term loans		$ 350,000,000
Subsequent Event | New Credit Agreement | Revolving Credit Facility
Subsequent Event [Line Items]
Line of credit facility maximum borrowing capacity		800,000,000
Subsequent Event | New Credit Agreement | Term Loan
Subsequent Event [Line Items]
Loan amount		$ 200,000,000
Scenario Forecast | New Credit Agreement
Subsequent Event [Line Items]
Capitalized loan costs			$ 2,100,000
Charges to write-off existing loan costs and other costs			$ 1,000,000