Investments - Summary of Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Investment [Line Items]
Marketable securities	$ 81,486	$ 41,496
Parent [Member]
Investment [Line Items]
Marketable securities	81,486	41,496
Equity method investments	7,101	9,007
Nonqualified retirement plan assets	5,662	5,310
Other investments	925	925
Total investments	$ 95,174	$ 56,738