Disaggregation of Sales - Schedule of Disaggregates of Net Sales of our Component Products and Real Estate Management and Development Segments (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation Of Revenue [Line Items]
Net sales	$ 516.8	$ 458.6	$ 415.0	$ 459.3	$ 414.1	$ 475.2	$ 528.6	$ 479.6	$ 1,849.7	$ 1,897.5	$ 1,820.1
Component Products
Disaggregation Of Revenue [Line Items]
Net sales									114.5	124.2	118.2
Real Estate Management And Development
Disaggregation Of Revenue [Line Items]
Net sales									96.4	42.1	40.0
Real Estate Management And Development | Land Sales
Disaggregation Of Revenue [Line Items]
Net sales									87.0	33.5	32.3
Real Estate Management And Development | Water Delivery
Disaggregation Of Revenue [Line Items]
Net sales									7.6	6.8	5.6
Real Estate Management And Development | Utility and Other
Disaggregation Of Revenue [Line Items]
Net sales									1.8	1.8	2.1
Security Products | Component Products
Disaggregation Of Revenue [Line Items]
Net sales									87.9	99.3	98.4
Marine Components | Component Products
Disaggregation Of Revenue [Line Items]
Net sales									$ 26.6	$ 24.9	$ 19.8