Investments - Summary of Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investment [Line Items]
Marketable securities	$ 74,907	$ 41,496
Parent [Member]
Investment [Line Items]
Marketable securities	74,907	41,496
Equity method investments	7,731	9,007
Nonqualified retirement plan assets	5,808	5,310
Other investments	925	925
Total investments	$ 89,371	$ 56,738