Cash Flow Information - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2019	Jun. 30, 2019	Jun. 30, 2018
Other Significant Noncash Transactions [Line Items]
Cash paid for interest		$ 26.9	$ 28.9
Net of capitalized interest		4.3	2.9
Line of credit facilities gross borrowings		150.0	0.0
Line of credit facilities gross repayments		33.0	53.0
Accrued construction costs		$ (15.5)	$ (4.6)
Common Stock
Other Significant Noncash Transactions [Line Items]
Conversion of units, shares issued (in shares)	6,250,000