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Investments - Summary of Investments (Detail) - USD ($)
$ in Thousands
Jun. 30, 2017
Dec. 31, 2016
Investment [Line Items]    
Marketable securities $ 72,162 $ 74,907
Parent    
Investment [Line Items]    
Marketable securities 72,162 74,907
Equity method investments 11,004 7,731
Nonqualified retirement plan assets 6,396 5,808
Other investments 3,834 925
Total investments $ 93,396 $ 89,371