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Investments - Summary of Investments (Detail) - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Investment [Line Items]    
Marketable securities $ 70,595 $ 74,907
Parent    
Investment [Line Items]    
Marketable securities 70,595 74,907
Equity method investments 8,360 7,731
Nonqualified retirement plan assets 6,186 5,808
Other investments 925 925
Total investments $ 86,066 $ 89,371