Capitalized Interest - Summary of Interest Costs Incurred, Capitalized, Expensed and Charged to Cost of Sales (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Capitalized Interest Costs Including Allowance for Funds Used During Construction RollForward
Interest capitalized, beginning of year	$ 5,583	$ 5,106	$ 4,434
Interest incurred	26,277	26,384	25,951
Interest expense	(25,081)	(24,185)	(21,707)
Interest charged to cost of sales	(2,625)	(1,722)	(3,572)
Interest capitalized, end of year	$ 4,154	$ 5,583	$ 5,106